I worked with the Dallas ISD for several years on garden programs and learned a lot about the laws regulating these programs. Just thought I'd save you some grief by sharing a little of what I learned.
To avoid any problems, let me urge you to get with the school's IPM (Integrated Pest Management) coordinator before you use any chemical of any kind on the gardens. It is actually illegal for you to use any kind of material recognized as a pesticide (that includes insecticides, miticides, rodenticides and herbicides) on a school property unless you are a licensed applicator. You could be fined. This includes fungicides and some types of fertilizers. And Rootone has a fungicide in it, so it is included.
You also want to check on the district's policy on the pressure-treated "green" CCA wood. Many districts have had it removed from their grounds and instituted new rules that forbid its use. Rock or steel borders hold up to kids' traffic well.
The organic products that are food material based; molasses, d-limonene/orange oil, cornmeal, baking soda, vinegar, etc. can be used without prior approval. Let me caution you that some children do react to cedar, so be careful if you use it as a mulch. Ask them if they are allergic if they are old enough to know. Vinegar can cause some kids to rash too. D-limonen is a solvent, so treat it like one...until you mix it with water and harmlessly pour it out on the ground!
For plant selection, try to get a copy of the Texas Smartcscape CD as it is most helpful with sun/shade, watering levels, size and bloom information and photos. Howard's book Plants for Texas is great too. I had kids grow carrots and they LOVED it.
You might incorporate the use of mulch vs. the lack of mulch as a part of your experiment. It so greatly affects compaction, erosion and moisture retention.
Pat yourself on the back, GREAT TEACHER! No matter whether the plants thrive or wilt, this program will do your kids a world of good, and they will always remember it. I still have kids tell me how much they enjoyed the programs, and that was years ago...they are in high school now.
I hope you find this material helpful. If you would like to talk more privately, feel free to PM me.