John Thompson lays it out in a well written post. This is one of the many problems that NCLB doesn't take into account:
"I earn my paycheck by "reading" teenagers. I probe the students' background knowledge to determine what information they have retained from previous years. More and more, it is clear that previous lessons have "gone in one ear, and out the other." As teachers feel increased pressure to "cover" the material, teaching for understanding has decreased.
The pace at which a class moves must be determined by the rate that students master skills and conceptual building blocks. Listen to the kids and they will teach you the rate at which the class must move. Assessment data can be invaluable, but there is no substitute for the professional judgement of an experienced teacher. And different children in different classes learn at varying rates. Each class always develops its own personality."
For those of you don't know what "curriculum pacing", here is a totally biased, but still appropriate description:
"Before NCLB, teachers had considerable control over the speed at which they presented the curriculum. After a new curriculum was adopted though, they had to move at a one-pace-fits-all because district tests had to be given at a certain time."