1. Build a bridge using popsicle sticks and assess its strength by putting weights on top.
2. Create a paper airplane and test different designs to see which one flies the farthest.
3. Design a parachute using a plastic bag and string and see how slowly it can land a small object.
4. Investigate which materials make the best insulators for keeping an ice cube from melting.
5. Construct a simple circuit using wires, a battery, and a light bulb to understand how electricity flows.
6. Build a tower using toothpicks and marshmallows and see how high you can make it before it collapses.
7. Explore the concept of buoyancy by building boats out of aluminum foil and testing how many pennies they can hold.
8. Experiment with magnets by testing which objects are attracted to them and which are not.
9. Create a pulley system using string and a toy car to understand how simple machines can make work easier.
10. Investigate the effects of different liquids on plant growth by setting up a simple hydroponics experiment.
11. Design and build a roller coaster using cardboard tubes and investigate how the height of the starting point affects the speed of the car.
12. Explore the properties of water by conducting an experiment to see how different objects float or sink.
13. Build a simple robot using craft materials and explore basic programming concepts.
14. Investigate the movement of shadows by building a sundial and tracking the changes in shadow position throughout the day.
15. Create a homemade lava lamp using oil, water, and food coloring to understand the concept of density.
16. Explore the concept of sound by building a musical instrument using everyday objects.
17. Design and build a structure that can withstand an earthquake simulation using toothpicks and marshmallows.
18. Investigate the effects of different forces on objects by designing and testing a mini zip line.
19. Create a mini greenhouse using a clear plastic container and observe how it affects plant growth.
20. Experiment with the effects of friction by building a ramp and testing how different materials make objects slide faster or slower.
21. Explore the concept of balance by building a seesaw using a ruler and small weights.
22. Investigate the properties of different types of soil by conducting a simple sedimentation experiment.
23. Build a model of the solar system using paper plates and learn about the different planets.
24. Experiment with the concept of density by layering different liquids with different densities in a clear container.
25. Design and build a simple water filter using materials like sand and gravel to understand the process of filtration.

These 25 First Grade STEM Challenges are a great way to engage young learners in hands-on, interactive learning experiences. They cover a range of scientific concepts and engineering principles, allowing students to explore and discover the world around them in a fun and engaging way.