I'd like to see some more support for the claim that NCLB contributed much for this.
When I was in middle school, my 7th grade teacher found a printed off copy of the Anarchist Cookbook of mine that a friend printed off and gave to me at school. This was a bit after Columbine, which meant I probably was going to be expelled for this sort of thing. I was lucky that that particular teacher was the one who found it. She was a former Army officer and, at least in this instance, was a good judge of character. She sat me down, sternly told me that she did not have the slightest inclination that I was planning anything beyond teenaged mischief, but that I could never bring anything like this to school again. She explained that I would be expelled for this sort of thing and that essentially I owed her. While I was an honors student, I did have a rap sheet 1, which would've surely meant automatic expulsion. I was extremely lucky that that teacher was reasonable; most were not.
If NCLB did anything, it may've amplified the trend, but that trend has been going for quite some time, I suspect.
1: I had jumped a kid earlier in the year. He was making fun of the fact that I and several other boys had recently lost our fathers. We explained that if he kept it up, that we would kick his ass. He kept it up and we obliged. Maybe it was due to this being the South, but no administrator or adult told me that I did anything wrong per se, only that they had to suspend me for two weeks. The most condemnation I received was from my football coach who was upset that he had to lose a starting player for two games; he advised me to take the kid off campus in the future (so kidnapping and assault).