Hi Kelly and Sarah,
I live in Maine where almost every school has a school based garden project. Most of these project started out small and then built upon them as the years went by with some very much integrated into the school curriculum. The Troy Howard Middle School in Belfast ME has a long standing program http://www.schoolgardenproject.com/
That said, I would start small. Here is a nice article about 'Creating a Schoolyard Mini-Garden'
The article gives beginning suggestions and includes some funding sources
'The creation of schoolyard gardens is a growing movement in the United States and around the world (Ballard, Tong, and Usher 1998; Pope 1998; Lewis 2004). It brings together all of the features of authentic hands-on science: Students can collect data on plant growth, observe the plant and animal interactions in the garden, and acquire a sense of nature and environmental issues. Here the author shares how easy it can be to start a schoolyard garden, using an in-class germination project as a starting point. With just a tiny plot of land, they created a mini-garden that infused third-grade students with a sense of pride and accomplishment."
Let me know if this is useful information!