Got some blacktop playground, 28 or so students and wondering how to garden?
Make Your Own Mobile Planter
Here's a YouTube from The People's Garden, and USDA experts at a DC school, working to make a mobile planter at a DC elementary school - from a 100 gallon plastic tank....
Not feeling crafty - and haven't got time to make a "self-watering" planter?
Then you can buy smaller EarthBoxes for about $60 online at http://earthbox.com/
If going outside seems too difficult and you want to maximize success for indoor gardening - try a Tower Garden https://www.towergarden.com/
Growing veggies, herbs and flowers aeroponically without soil might just be the approach that you need to get your class going growing. The tower is easy to assemble and works with very little water/nutrients and a recirculation pump. You can then grow vegetables indoors at a time that suits you and your class. Costs about $ 550 - 1000 for the full kit.
See how the Tower Garden works commercially at Chicago's O'Hare airport - delivering fresh local produce to airport staff and travelers.
Easy Care Native Plants for Low-Watering
The tank mobile planters, EarthBoxes and Tower Gardens work well for growing vegetables and flowers.
If you are not at school during the summer and need low-maintenance watering - try planting your Earthbox or planter with native plants such as Rudbeckia Black-eyed Susan and Echinacea Purple Coneflowers. These flowers will attract lots of pollinators and are "easy-care".
Got the box and now wondering what to teach?
Earthbox sells curricula pre-K-12 linked to standards and STEM
With your Tower Garden - check out ideas for teaching from Stephen Ritz and the Green Bronx Machine http://greenbronxmachine.org/