A simple way would be to individually make the specimen plants with either just a number, or with their botanical / latin name and possibly their common name as well, e.g.

"Quercus virginiana"
Live Oak

And at the start of the 'trail head' or whathaveyou, some starting point, maybe make a plaque or display that lists the plants by number and maybe goes into more depth about their specifics. Native plant here, butterfly plant here, etc.

Also, this sounds like something to bring up with the school. Not that you're asking for donations, but you could involve them. Get ideas from students and teachers. Maybe they could create the display to be mounted in the garden.