Rockwool is the growing medium used in a Tower Garden. There are several different methods for starting seeds other than the one that comes with the Tower Gardens. If you would like to give your students some help, here are three methods.
https://www.keepitwatered.com/seed-starting-procedure (The method I use)
https://www.naturalmomsblog.com/start-seeds-tower-garden.html
https://www.trees.com/gardening-and-landscaping/rockwool-cubes
This page is a companion article for the 9th-12th grade life skills curriculum. More info can be found on the Tower Garden Curriculum page.