You need to be running Ubuntu 11.10 (oneiric) or 11.04 (natty). Packages for earlier releases (maverick and lucid) will be built soon.
Open the Ubuntu Software Center. Choose Edit > Software Sources... Click Other Software > Add..., enter as the APT line:
ppa:schooltool-owners/dev
And click Add Source.
Then search for “SchoolTool” in the searchbox at upper right in the Software Center and click Install next to the SchoolTool entry.
You have to add the SchoolTool flourish PPA to your software sources:
$ sudo add-apt-repository ppa:schooltool-owners/dev
$ sudo apt-get update
Then install the schooltool package:
$ sudo apt-get install schooltool
After installation, the schooltool server will be started at http://localhost:7080 .