I´m not sure whether your plan is feasible, since planting something virtually maintenance free and able to choke down weeds is quite difficult to achieve.

One option for you, and since this is a school, is to use it as an opportunity to teach the kids something. Maybe what you could do was:

1 - Remove any plants planted that you want to keep

2 - Lay down lots of newspaper and cardboard and build a type of lasagna garden bed. There is a forum specifically for this method and there is also an interesting discussion of it in the cottage gardens forum. The kids could bring the newspaper and cardboard from home and help build the layers. This would also offer the biology teachers the chance to teach them a bit how Mother Nature works.

3 - Once the bed is ready, replant the plants you saved and add other easy care ones. Options for your warm climate are succulents, cacti and ornamental grasses. Maybe each kid could donate a plant (don´t know how many kids there are in the school and the size of the beds), according to the directives you set. This wouldn´t cost much for the families but would give the kids a sense of ownership they will lack if you just get the plants from a garden centre. They will then be able to track the progress of his/her own plant, as well as the others.

4 - Prepare to have at least minimum care during the Summer holidays, otherwise this would just be a waste a time. Isn´t there a janitor or security officer who might be able to water? If this is not the case, consider investing in a watering system which can be operated by a small programmable computer. If you use easy care plants like I mentioned above you should be able to get away with it for a couple of months without much care anyway.

I don´t know if I´ve helped, but this is how I would approach the project, if it was mine.

Eduarda

Great advise from Eduarda,
I would like to add and highly recommend the use of MULCH
ALOT of it. I'm not talking about a thin layer just to cover. I'm talking at least 4 inches. THe more the better.

It will help in the prevention of most weeds and the ones that insist on trying too grow there it so much easier to pull them out.

Mulch will help with the amount of watering.
I'm in North Dallas and since I have learned this I have not had to water my flower beds but just once during the bad draught summer year before last and not at all this summer. It all survive on what rain we got.

Visit the Lady Bird Johnson WIld Flower Center on the web and see the hardy, drought, resistant plants they grow and suggest.

Also Our Garden club will have plants to donate in the Spring so let me know if you need anything then.