06.25.08

Math and reading test scores are up in most states since the No Child Left Behind law took effect in 2002, but it's impossible to know how much credit the law deserves, a new report says.

In an exhaustive study released Tuesday, the Center on Education Policy also concluded that the historically wide achievement gap between black and white children has generally narrowed in many states - exactly what NCLB supporters said they wanted to achieve when President Bush signed the law.

But the law's contributions are hard to measure because a number of states already were taking steps to boost reading and math, the study's authors say. And because every public school falls under the law, there is no group of students to use for comparison, they said.