Typically, it's the liberals who reject NCLB, but here's why lots of conservatives dislike the bill as well, primarily because it puts the federal government in charge of education, not the states and localities, and also because it emphasizes equality of outcomes instead of equality of opportunity. Both are long-term recipes for disaster, however well intentioned the bill might be in the short run.
http://www.weeklystandard.com/Content/Public/Articles/000/000/014/118xfsjy.asp?pg=2
http://www.american.com/archive/2007/september-0907/defining-achievement-downward