From what I know about local schools today (two of my family members are teachers), they take reports of odd behavior seriously and document it. Most of the time the police are not notified unless something severe happens. Then the whole history is communicated to them.

I am sure that with all the statements made about him so far (one guy said on the NBC news that he looked over his shoulder when he was at the dry-erase board to keep an eye on Loughner, others say the knew he was gonna show up one day with a weapon and take everyone out) his schools had to notify the police at one time or another.

It's not always clear who is 'mentally ill' and who is gonna snap because they just got fired. In so many other cases, people say they were clueless about a shooter until after the damage was done.