Each box has a robot to assemble that illustrates a STEM principle, complete with a battery and an Arduino microcontroller. Our box had the infrared turret to illustrate the principle of infrared communication. It's expensive, but the price-per-payoff valuation is worth it—the STEM principle it illustrated was interesting, the build process was engaging without being frustrating, and the project itself was very fun. ★ Alternatives: For much younger kids, Little Passports has an Early Explorers box ($20/month) aimed at children as young as 3. Steve Spangler's Science Club STEM kits ($33) feature classic projects, like a marshmallow masher, that you could Google online and replicate with items you have at home.