15 Mind-Blowing STEM Activities Your Tweens Will Actually Love

There are several STEM challenges appropriate for 10-12-year-olds. These challenges can be completed individually or even as teams. A few challenges work best if done as a team. Depending on the number of students, you can have teams of two or even teams of four or five. Let them work through the challenge. These challenges are meant to be fun. Beware, the noise level could get loud.

Maximum-Weight Paper Bridge

The Tween Twist: Instead of just laying a piece of paper across a gap, tweens must use structural engineering principles (like tension, compression, and load distribution) to see how many real pounds or heavy cans a single sheet of paper can hold.

The Mission:

Design and build a bridge spanning a 6-inch gap using only one sheet of paper and minimal tape, engineered to hold the absolute maximum amount of weight possible before collapsing.

Supplies Needed:

• 1 standard sheet of printer paper (8.5 x 11 inches)
• 3 inches of masking tape or painter’s tape
• 2 large books or wooden blocks (to act as the bridge abutments/supports)
• 1 ruler or measuring tape (to ensure a strict 6-inch span)
• Weights for testing (canned goods from the pantry, coins in a plastic cup, or small hand weights)

The Blueprint (How to Build It):

• Set the Span: Place two heavy books exactly 6 inches apart on a flat surface.
• Manipulate the Material: Tweens cannot alter the paper’s mass, but they can alter its structural integrity. They should experiment with folding the paper into tight accordion pleats (corrugation), rolling it into tight cylinders to create a beam bridge, or folding the edges upward to create rigid side walls (girder bridge).
• Secure the Structure: Use the 3 inches of tape strictly to secure the folds or anchor the ends to the support blocks if your design calls for it.
• The Ultimate Weight Test: Place an empty plastic container on top of the bridge and slowly add heavy coins, or carefully stack pantry cans one by one directly onto the center of the span. Record the exact weight held right before the paper buckles.

Suspension vs. Simple Beam:

The Tween Twist: This is a direct comparative challenge. Tweens will build two distinct styles of bridges using identical span constraints to analyze firsthand how suspension cables distribute tension versus how a solid beam handles compression.

The Mission:

Build a standard Beam Bridge and a functional Suspension Bridge across a 12-inch gap, then stress-test both structures to see which design rules supreme under a heavy load.

Supplies Needed:

• Strong corrugated cardboard (cut into two 3×14 inch strips for the bridge decks)
• 4 large, unopened food cans or heavy bricks (to act as the anchor points/towers)
• 1 roll of strong, non-stretchy kitchen twine or thick yarn (for the suspension cables)
• Heavy-duty tape (duct tape or strong packing tape)
• 1 ruler or measuring tape
• Testing weights (a plastic cup filled with pennies, small stones, or small hand weights)

The Blueprint (How to Build It):

• Test the Simple Beam Bridge: Place two cans exactly 12 inches apart. Lay one piece of cardboard across them so it spans the gap like a flat plank. Place weights directly on the center of the span until the cardboard bends, buckles, or slips off. Note how quickly a simple beam fails across a wide gap without central support.
• Build the Suspension Towers: To build the suspension bridge, place the remaining two cans/bricks on either side of the gap. Tape a sturdy wooden skewer, pencil, or cardboard pillar vertically to each can to act as your high towers.
• Run the Cables: Cut a long piece of twine to act as your main deck support. Securely tape the cardboard bridge deck to the underside of the main string. Drape the string over the top of your vertical towers on both sides, pulling it taut, and anchor the string ends firmly to the table surface behind the cans using heavy-duty tape.
• The Tension Test: Place your testing weights on the suspension deck. Watch how the downward forces (compression) on the deck are transferred up the vertical strings, into the main cable, and securely down into the table anchors (tension). Compare the maximum weight held by both designs.

Ultimate Marshmallow Tower

The Tween Twist: Instead of just building a tall tower, the structure must be engineered to support weight (like a small book or a tennis ball) at the top for at least 10 seconds.

The Mission:

Build the tallest possible freestanding tower that can support a designated weight using only spaghetti and marshmallows.

Supplies Needed:

• 1 box of uncooked spaghetti noodles
• 1 bag of large marshmallows (or mini marshmallows for a harder structural challenge)
• 1 measuring tape
• A test weight (e.g., a tennis ball or small paperback book)

The Blueprint (How to Build It):

• Design the Base: Break or keep spaghetti noodles whole to construct a wide, stable foundation (triangles and pyramids work best for distribution of mass).
• Connect the Joints: Use marshmallows as the structural hubs, piercing them with the spaghetti strands.
• Build Upward: Carefully layer geometric tiers upward, ensuring the tower remains balanced and vertical.
• The Stress Test: Place your test weight on the very top marshmallow to see if your engineering holds under pressure.

Jet-Propelled Balloon Car

The Tween Twist: Instead of just making a car that rolls forward a few inches, tweens must experiment with jet propulsion, weight distribution, and nozzle sizes (changing the diameter of the exhaust straw) to optimize their car for maximum distance or raw speed.

The Mission:

Apply Newton’s Third Law of Motion (action and reaction) to engineer a lightweight vehicle that uses air pressure from a balloon to launch itself across a room.

Supplies Needed:

• 1 lightweight chassis base (a small piece of sturdy cardboard, an empty juice box, or a flat plastic bottle)
• 4 bottle caps or old CDs (for wheels)
• 2 wooden skewers or bamboo rollers (for axles)
• 2 wide plastic smoothie straws (to use as axle sleeves/bearings)
• 1-2 large, high-quality latex balloons
• 1 standard drinking straw or extra-wide boba straw (the jet nozzle)
• Rubber bands or painter’s tape
• Hot glue gun or strong tape

The Blueprint (How to Build It):

• Construct the Axle System: Flip your chassis over. Cut two pieces of the wide smoothie straw slightly wider than your car base and glue them parallel to each other on the front and back of the chassis. Thread your wooden skewers through these straw sleeves.
• Mount the Wheels: Carefully poke a hole through the exact center of your four bottle caps. Attach them to the ends of the wooden skewers, securing them with hot glue so the axle and wheels turn perfectly as one unit.
• Assemble the Jet Engine: Take your balloon and slide the neck over one end of your standard drinking straw. Wrap a rubber band or piece of tape tightly around the connection point so that when you blow into the other end of the straw, the balloon inflates without air leaking from the seal.
• Secure the Engine: Tape the straw completely flat along the top of your car chassis. Ensure the balloon sits toward the front of the car, and the open tail end of the exhaust straw extends out past the rear axle.
• Inflate and Launch: Pinch the end of the straw shut, blow through it to fully inflate the balloon, place the car on a hard, smooth floor, and release. Tweens can swap to wider or narrower exhaust straws to see how changing the air release rate affects their vehicle’s acceleration versus its total distance.

Rubber Band Powered Car

The Tween Twist: Tweens must experiment with wheel traction and friction. If the wheels spin wildly in place, they have to figure out how to add grip (like wrapping rubber bands or electrical tape around the CD edges).

The Mission:

Apply Newton’s Third Law of Motion to design a functional vehicle that uses potential energy stored in a twisted rubber band to launch itself forward.

Supplies Neeed:

• Corrugated cardboard (cut into a 4×6 inch rectangle for the chassis) or a plastic bottle
• 4 old CDs or DVDs (for wheels)
• 2 wooden dowels or bamboo skewers (axles)
• 2 thick plastic drinking straws (axle sleeves)
• 2-3 strong rubber bands
• 1 hot glue gun or heavy-duty tape

The Blueprint (How to Build It):

• Build the Chassis: Cut a wide rectangle out of one end of your cardboard chassis to expose the rear axle where the rubber band will wrap.
• Attach Axle Sleeves: Glue two pieces of plastic straw across the bottom of the cardboard chassis to act as bearings.
• Mount the Wheels: Thread the wooden skewers through the straws. Center the CDs on the ends of the skewers and hot glue them securely so the axle and wheels turn together.
• Install the Motor: Anchor one end of the rubber band chain to the front of the chassis. Wrap the loop at the other end around the center of the rear axle hook (a small piece of toothpick glued to the axle works perfectly).
• Wind and Launch: Roll the car backward to wind the rubber band tight around the rear axle, place it on a smooth surface, and let go.

Kinetic Marble Run

The Tween Twist: The goal isn’t just to get the marble to the bottom—it’s to design the slowest track possible using friction, loops, and obstacles, keeping the marble moving for a minimum of 10 seconds.

The Mission:

Use physics, gravity, and momentum to engineer an intricate wall-mounted or freestanding track that safely delivers a marble to a target cup.

Supplies Needed:

• Cardboard tubes (paper towel, toilet paper, or shipping tubes)
• Paper plates or plastic cups
• Painter’s tape (wall-safe) or hot glue
• Marbles
• Scissors or a utility knife

The Blueprint (How to Build It):

• Prep the Tracks: Cut cardboard tubes in half lengthwise to create open U-shaped tracks and channels.
• Map the Path: Anchor the starting track high up on a wall, vertical cardboard backing, or large box using tape.
• Engineere Obstacles: Cut slots into paper plates to create spiral funnels, or tilt your tracks at slight angles to deliberately slow down the marble’s velocity.
• Test and Tweak: Drop the marble from the top and adjust the slopes, drop points, and angles until the marble consistently hits the landing cup at the bottom.

Desktop Siege Trebuchet

The Tween Twist: Unlike a simple catapult that relies on the elasticity of a rubber band, a trebuchet relies entirely on gravitational potential energy and a falling counterweight. Tweens must figure out the perfect ratio between the weight of their projectile and the weight of their counterweight to fling an object across the room.

The Mission:

Apply the physics of levers and counterweights to construct a functioning medieval trebuchet capable of launching a small projectile on a flat trajectory.

Supplies Needed:

• 10-12 large popsicle sticks or wooden craft sticks
• 3-4 wooden skewers or thick toothpicks
• Hot glue gun and glue sticks
• 1 large metal bolt, a stack of heavy washers, or a roll of coins (the counterweight)
• A short piece of string or yarn (approx. 6 inches)
• A small piece of fabric, leather, or duct tape (to form the launch pouch)
• 1 plastic bottle cap
• Projectiles (mini marshmallows, pom-poms, or crumpled foil balls)

The Blueprint (How to Build It):

• Build the A-Frame Base: Glue your popsicle sticks together to form two identical triangle frames (“A-frames”). Connect these two vertical triangles with three or four horizontal cross-sticks on a flat surface to create a wide, stable base cube.
• Craft the Pivot Arm: Take a long popsicle stick to act as your lever arm. Drill or poke a clean hole through the stick about 1/4 of the way down from one end. Thread a wooden skewer through this hole; this skewer will rest horizontally across the peak of your A-frame base as the axle pivot point.
• Load the Counterweight: Attach your heavy metal bolt or stack of washers securely to the shorter end of the pivot arm using hot glue or wire.
• Attach the Launch Sling: Glue your plastic bottle cap to the long end of the arm, or tie your string and fabric pouch to the tip to create a traditional swinging sling release.
• Fire the Engine: Pull the long arm down, placing your light projectile in the pouch or cap. Hold it, release, and watch how the heavy, falling short end instantly propels the long end upward and forward.

The Floating Dry-Erase Drawings

The Tween Twist: Instead of just making a drawing on paper, tweens will dive into chemistry, using the hydrophobic properties of dry-erase ink and the concept of buoyancy to make their hand-drawn stick figures peel off a surface and swim intact.

The Mission:

Use solvent solubility, density, and surface tension to lift a marker drawing completely off a surface and control its movements on water.

Supplies Needed:

• A smooth, non-porous glass plate, ceramic bowl, or smooth glass baking dish (white or transparent works best)
• Brand new, high-quality dry-erase markers (standard Expo markers work perfectly; metallic or off-brand markers often fail)
• Lukewarm or warm water
• 1 plastic straw (for manipulating the floating shapes)

The Blueprint (How to Build It):

• Draw the Subject: On the completely dry surface of your plate or bowl, draw a bold, solid figure (a stick figure, an airplane, or a spider). Make sure all lines are connected and filled in thickly without gaps.
• Let It Set: Let the ink dry completely for 30 to 45 seconds so the alcohol solvent can evaporate, leaving behind a solid, plastic-like film of pigment and silicone polymer.
• The Slow Pour: Tilt your plate at a very slight angle. Slowly and gently pour the warm water into the corner of the plate, letting it gradually creep toward your drawing. Do not pour the water directly on top of the ink.
• Watch the Lift: As the water moves under the drawing, the buoyant force of the water will overcome the weak bond between the silicone ink and the smooth glass, lifting the drawing cleanly to the surface.
• Control the Motion: Tweens can use their straw to gently blow air across the surface of the water, racing their floating drawings against each other without breaking them.

Pressure-Powered Bottle Rocket

The Tween Twist: This challenge focuses heavily on aerodynamics, chemical reactions, and volume. Tweens will test how changing the volume of fuel (the water-to-air ratio or the vinegar-to-baking-soda ratio) alters the maximum altitude of the launch due to changing pressure limits.

The Mission:

Utilize pressurized gas to build and safely launch a lightweight aerodynamic rocket into the air from an outdoor testing zone.

Supplies Needed

• 1 empty 2-liter soda bottle (the rocket body)
• Sturdy cardboard or plastic sheeting (to cut out 3-4 stability fins)
• 1 tennis ball or plastic cone (for the nose cone weight)
• 1 clean cork that fits tightly into the mouth of the soda bottle
• 1 standard hand-operated bicycle pump with a needle adapter OR baking soda and white vinegar
• Duct tape or hot glue

The Blueprint (How to Build It):

• Design for Stability:
  1. Turn your soda bottle upside down so the spout points downward (this spout is your engine nozzle). Tape or glue 3 or 4 cardboard stability fins symmetrically around the lower third of the bottle. Tape a tennis ball securely to the top (the bottom of the bottle) to act as a weighted nose cone.
  2. Prepare the Launcher (Mechanical Method): Push the metal needle adapter of your bicycle pump straight through the center of your rubber or wooden cork until it pokes out the other side.
  3. Load the Fuel: Pour water into the bottle until it is roughly 1/3 full. Push the cork with the pump needle tightly into the mouth of the bottle.
  4. The Launch (Outdoor Activity Only): Take the setup to an open backyard or park. Stand the bottle upright on its fins on a flat surface, or rest it against a stable box angled away from people. Step back and begin pumping air into the bottle. As pressure builds inside, the cork will suddenly pop out, releasing the pressurized water downward and launching the rocket into the sky.
     (Alternative Chemical Fuel: Wrap 2 tablespoons of baking soda tightly inside a piece of paper towel, pour 2 cups of vinegar into the bottle, quickly drop the paper towel packet inside, firmly press the plain cork into the opening, flip it onto its launchpad, and stand back immediately as gas expands.)
     

Overnight Supersaturated Crystal Geode

The Tween Twist: Instead of waiting weeks for standard sugar crystals to form, tweens will dive into chemistry using Borax or alum to create a rapid, highly dense supersaturated solution that grows complex, shimmering crystalline structures overnight inside a real eggshell.

The Mission:

Master the relationship between temperature and solubility to force dissolved minerals out of a liquid solution and lock them into a hard geometric lattice.

Supplies Needed:

• 2-3 clean, empty eggshell halves (washed out carefully)
• Craft glue and a small paintbrush
• Borax powder (laundry aisle) or Alum powder (baking aisle)
• Boiling water
• A glass jar or heat-safe measuring cup
• Food coloring

The Blueprint (How to Build It):

• Seed the Crystals: Paint the inside of your clean eggshell half with a thin layer of craft glue. While the glue is wet, sprinkle a handful of Borax or alum powder directly onto it until the interior is coated. Let it dry completely. These loose powder grains act as “seed crystals” for the solution to latch onto.
• Mix the Solution: Boil 2 cups of water. Slowly stir in your powder (Borax or alum) one tablespoon at a time. Keep stirring until the water is completely clear, then add more. Stop adding powder only when it refuses to dissolve anymore and starts settling at the bottom. This means your solution is officially supersaturated. Stir in your food coloring.
• The Submersion: Let the colored liquid cool slightly so it doesn’t dissolve your eggshell’s glue. Carefully lower your seeded eggshell into the jar so it is completely submerged, open side facing up.
• Watch It Grow: Leave the jar completely undisturbed in a warm room overnight. As the water cools, its capacity to hold the dissolved powder drops drastically, forcing the minerals to rapidly crystallize onto your seed grains. Gently lift out your stunning crystal geode the next morning.

Zero-Crush Bungee Egg Drop

The Tween Twist: Dropping an egg inside a padded box is too easy for tweens. In this version, the egg must be suspended out in the open, relying entirely on the elasticity and shock absorption of rubber bands to act as a bungee jump, stopping the egg mere millimeters from the ground without it cracking.

The Mission:

Apply momentum, kinetic energy transfer, and impulse physics to design a vehicle that decelerates an egg safely before it impacts a hard surface.

Supplies Needed:

• 1 raw egg
• 1 open plastic cup or small plastic basket (the carriage)
• A large assortment of thin rubber bands or elastic hair ties
• Popsicle sticks or cardboard scraps (to build an external frame)
• Duct tape or hot glue
• A high drop point (like a ladder, balcony, or staircase)

The Blueprint (How to Build It):

• Build the Outer Exoskeleton: Construct a rigid box frame or outer cage out of popsicle sticks and hot glue. This cage needs to be significantly larger than your plastic egg carriage.
  Suspension Rigging:** Do not pad the egg. Instead, punch holes around the rim of your plastic egg carriage. Use rubber bands to suspend the carriage dead-center inside your rigid popsicle-stick cage. The carriage should float in the middle, held taut by elastic bands stretching to all eight corners of the frame.
• Secure the Cargo: Place your raw egg securely into the floating carriage (you can use one piece of tape to keep it from flying out of the top).
• The Drop Test: Drop the cage from your designated height. When the outer frame hits the ground, watch how the kinetic impact force is absorbed by the stretching rubber bands instead of being transferred directly to the egg shell. Tweens can adjust the tension of the bands to see how it alters the deceleration rate

The Load-Bearing Gumdrop Geodesic Dome

The Tween Twist: Instead of building a simple cube, tweens will use advanced architectural geometry to build a dome out of repeating triangles. They will then stack heavy books on top of the hollow dome to see how curved geometric structures distribute immense weight.

The Mission:

Explore architectural engineering by assembling a series of interlocking triangles that distribute compression forces evenly across an entire dome surface.

Supplies Needed:

• 1-2 boxes of toothpicks
• 1 bag of firm gumdrops or spice drops (mini marshmallows work but collapse under heavy weight)
• A flat piece of cardboard (to use as a building platform)
• Heavy books (for the ultimate load test)

The Blueprint (How to Build It):

• Build the Pentagons: A true geodesic dome relies on a mix of pentagons and hexagons. Start by connecting 5 toothpicks with 5 gumdrops to form a flat pentagon. Repeat this to create 5 or 6 identical pentagons.
• Raise the Triangles: Push toothpicks upward from the corners of your flat shapes, pointing them inward to form 3D pyramids. Join the points at the top with a central gumdrop.
• Interlock the Base: Connect these modular geometric pyramids together in a circular ring on your cardboard base to form the bottom tier of your dome.
• Close the Roof: Step the layers inward, bridging the gaps with horizontal toothpicks until the dome closes gracefully at the very top apex.
• The Weight Test: Gently place a flat piece of cardboard across the top of your hollow dome, then slowly stack heavy books on top one by one. Tweens will watch how the weight pushes downward and outward through the network of triangles, allowing a fragile structure to hold surprising mass.

Mentos & Coke Fountain Showdown

he Tween Twist: This is not just a backyard trick. Tweens will treat this as a true fluid dynamics experiment. They will test how different nozzle shapes (like a tiny pinhole vs. a wide slit cut into a bottle cap) or different soda temperatures affect the height and velocity of the geyser.

The Mission:

Investigate physical nucleation, gas expansion, and the Venturi effect by engineering a controlled delivery system for a rapid chemical-physical reaction.

Supplies Needed:

• 2-3 brand-new, unopened 2-liter bottles of Diet Coke (Diet Coke works best because it contains aspartame and potassium benzoate, which lower surface tension, and it isn’t sticky when it cleans up)
• 1-2 rolls of mint Mentos candies
• 1 piece of smooth paper rolled into a tube (just wide enough to hold a stack of Mentos)
• 1 index card
• Spare 2-liter bottle caps (for altering the nozzle size)
• A drill or hammer and nail (adult supervision required to modify the caps)

The Blueprint (How to Build It):

• Prep the Launch Cap: Take a spare bottle cap and use a drill or nail to poke a small, precise hole directly through the center. (A smaller nozzle forces the escaping liquid into a high-pressure jet stream, launching it significantly higher).
• Load the Magazine: Roll a sheet of paper into a tight tube and stack 5 or 6 Mentos candies inside it. Place your index card flat over the bottom opening of the tube to act as a trapdoor.
• Set Up the Launchpad: Take your Diet Coke outside and set it on a flat, open area of grass. Unscrew the main cap. Place your index card (with the loaded Mentos tube sitting on top of it) directly over the open mouth of the soda bottle.
• The Drop: Line up the paper tube perfectly with the bottle opening. Quickly pull the index card out from between them like a magician pulling a tablecloth. The Mentos will drop into the soda simultaneously.
• Screw and Run: Instantly screw your modified, small-hole launch cap onto the bottle and step back quickly. The microscopic pits on the surface of the Mentos candies will instantly pull the dissolved carbon dioxide gas out of the liquid, causing a massive, pressurized explosion of foam through your engineered nozzle.

The Wire Water Strider

The Tween Twist: Instead of just talking about bugs, tweens will use engineering to mimic biomimicry. They must manipulate a piece of wire to create a “robot bug” that stands perfectly on top of water, relying entirely on surface tension without breaking the water’s molecular skin.

The Mission:

Apply principles of fluid mechanics, weight distribution, and surface tension to make a dense metal wire float effortlessly on water.

Supplies Needed

• Thin, lightweight copper or floral wire (24 to 28 gauge works best)
• Wire cutters or sturdy scissors
• 1 wide bowl filled with clean water
• Dish soap (held back for the ultimate disruption test)

The Blueprint (How to Build It):

• Cut the Chassis: Cut a 6-inch piece of thin wire to act as the body and legs of your insect.
• Engineer the Legs: Twist the wire to form a central body with 4 to 6 long, symmetrical legs stretching outward.
• Optimize Weight Distribution: Tweens must bend the very tips of the wire legs into flat, wide loops or horizontal feet. The secret to making metal float is maximizing the surface area of the feet so the bug’s weight is distributed evenly across the water molecules.
• The Launch: Very gently and horizontally lower your wire insect onto the surface of the water. If designed correctly, you will see the water’s surface dimple under the feet without the wire breaking through and sinking.
• The Surface Tension Collapse: Once it floats, add just a single drop of dish soap to the far corner of the bowl. Tweens will watch in amazement as the soap molecules instantly disrupt the water’s surface tension, causing the wire bug to plunge to the bottom immediately.

Floating Electromagnetic Compass

The Tween Twist: Tweens will look past simple bar magnets to build a temporary navigation tool. They will use a battery and a copper coil to induce a magnetic field, turning a standard steel sewing needle into a magnetized pointer that aligns perfectly with Earth’s magnetic poles.

The Mission:

Explore electromagnetism and geomagnetic fields by creating a functional, floating compass from raw household components.

Supplies Needed:

• 1 steel sewing needle
• 1 strong neodymium magnet (or a AA battery and a small strip of aluminum foil to use the electromagnetism method)
• 1 small piece of cork, a slice of a pool noodle, or a flat piece of styrofoam
• A shallow bowl filled with water
• A smartphone with a digital compass app (to verify accuracy)

The Blueprint (How to Build It):

• Magnetize the Needle: Stroke a strong magnet down the length of the steel needle in one direction only, repeating this motion 30 to 40 times. (To use the advanced electromagnetic method, wrap a piece of thin insulated wire around the needle 20 times and touch the bare wire ends to the positive and negative terminals of a AA battery for 10 seconds to align the iron atoms inside the steel).
• Assemble the Float: Push the needle horizontally through the top of your small piece of cork or styrofoam disc. The needle needs to sit completely balanced on top of the float.
• Deploy the Compass: Carefully place the cork float into the center of your shallow bowl of water. Make sure there are no metal objects or computers nearby to interfere with the test.
• Watch the Alignment: The water eliminates friction, allowing the needle to spin freely. Watch as the needle slowly rotates on its own, locking into a strict North-South axis.
• Test the Field: Bring a metal object near the bowl to watch the needle deflect, then remove it to watch the compass automatically recalibrate itself back to Earth’s magnetic north.

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