First thing I would suggest is to create a template for the first school, get the thoughts and subthoughts just the way you want them, and then multiple select, Copy Thoughts, and Paste them 11 times (there are more details in other forum posts on how to do this). That way you are not duplicating work, and they are all uniform.
If you plan to use this as a standalone brain, I'd also suggest that you create 12 types, one for each school. That way you can easily run reports for the to-do's to narrow things down. You can also color code them, so if you have one to-do list with your actions for the schools all under that list you can tell at a glance which one is which. However, if you plan to use your brain for other things as well, its a lot of thought types, and may possibly create a glut of types.
Since one thought can have multiple parents, I would recommend you try having one consolidated to-do list, with all the upcoming items, and then also link the items to a to-do list for each school. You can pin the consolidated list up at the top, so it would be easy to create a child thought from your School to-do list, and then drag another parent link to the consolidated to-do list pin.
Take all this with a grain of salt though. You may go through the setup and find something else works best for you. Don't be afraid to change things as you go along, it's very forgiving.
I've included an example, because sometimes it's easier to see than create a mental picture.
Java SE 6