I've also been very worried about this happening. Any school system, or individual school would be a very pleasing target for multiple reasons. It's like a ball sitting on a tee waiting to be hit.
I tend to agree with sgtbono that it would be the biggest mistake terrorists could possibly make.
I'm concerned that we have allowed mosques in this country. I was not concerned before 9/11 but by midnight on 9/12 after just a bit of reading on the internet I became convinced that islam should not exist in the US.