Looking for a free STEM activity for the elementary classroom? Teachers are loving STEM because it's fun, hands-on, and engaging. The challenges are great for team building. This challenge is free and easy to implement. Great for 1st, 2nd, 3rd, and 4th graders. I usually use this challenge for back to school stem, but it can be done at any time. Students will have a great time working together to discuss, design, build, and reflect.