The elementary school that my youngest is at installed a garden 2 years ago and it's the highlight of the school.
One of the issues was making the garden ADA compliant, which meant building in raised beds and providing enough room between the beds for wheelchairs to maneuver. It actually makes the gardens easier for everyone to enjoy and gives lots of space for the kids to gather 'round and participate.
The garden has 2 raised beds that are 4 ft x 8 ft, a "three sisters" ground-level patch of corn, beans and squash, a 12-foot diameter geodesic dome built from tree branches that supports vines and hanging gourds, a sunflower patch and a pre-school wild flower garden. There are also 24 stools that are made of slices of a giant log so there is an outdoor learning space.
The beds themselves took about $900 in materials to build and the PTA paid for those. A local garden center helped donate and deliver fill for the beds. A bunch of parents (including dads) actually bought the lumber and built the beds and several families spent a weekend installing them. The students helped plant seeds into the beds (some classrooms started seedlings indoors) and a group of families signed up to water and weed over the summer and harvest what they wanted. It's a neighborhood school so there were plenty of volunteers for that. At the end of the summer, the school's back-to-school family picnic included foods made from the garden's vegetables.
Last year, they rotated the crops a bit, added the dome (which was an Eagle scout project for a boy in town), turned one of the beds into a fairy garden (huge hit with the kids), and added a pretty picket fence that families came out and painted on a Saturday.
If you're on Facebook, search for FARM - Fundamentals of Agricultural Resource Management - it's a page started by one of the parents who helped build the outdoor classroom and has lots of pictures, ideas and links. There are also grants available for installing school gardens - if you do a search you may find more info on that.
These websites are also great:
https://edibleschoolyard.org/
http://www.growtolearn.org/
http://www.kidsgardening.org/school-gardening
As you can see, I'm a huge, raving fan of school gardens. I hope you run with your idea and get the support that you need from the school administration, faculty, staff, and families.