| Sorry you haven't had any responses. I guess it's hard for people like me (with no experience) to gauge what these students are capable of. Tomatoes are really easy. I stick them in the ground, put 2 (medium and large) tomato cages around them, come back in a couple of months and harvest. There's really nothing to it except the harvesting. And my 2 and 4 year-olds LOVE to pick tomatoes. It's almost their favorite in the garden. Squash/pumpkins are the easiest foolproof plant, but they take up a LOT of space, and their vines might get stepped on. Not bothered by bugs or slugs and guaranteed to grow. Perhaps you can put in some mini-pumpkins, just a couple plants would give enough pumpkins for the whole class. You would probably want to plant in the late school year and harvest in the next fall. For flowers, zinnias are cheap and easy, troublefree and bloom for months and months. Pansies will bloom through the winter when not much else is going on and just need a bit of water. Cornflowers easy.
Are you doing perennials at all or only annuals? There are tons of easy beautiful perennials, but they don't necessarily have a long bloom time. How about planting star jasmine (trachelospermum) on an trellis or obelisk (or upside down, staked tomato cage) for a tower of fragrance? It's an evergreen climber with the most gorgeous fragrance for months in late winter and early spring when not much else is going on. Surprisingly tough and easy, grow it on anything and in a couple of years it will take off and everyone will love it.
How about hens-and-chicks? Super easy, take drought, always making babies which can be pulled off and planted for more. You can send some babies home with each student and they're guaranteed to grow at home. Take an amazing lack of water. I'm not usually in this forum, so I hope this isn't too late to help you. | 
