WASHINGTON — President Barack Obama asked Congress today to rewrite the nation’s main education law before the new school year starts in September, setting an ambitious timetable for lawmakers whose primary focus now is on budget cuts and the deficit.

He also issued his most detailed outline yet for changes to the No Child Left Behind law.

Obama said the law, enacted in 2002 under George W. Bush, got some things right but that it also got some things wrong.

“The goals of NCLB were the right goals,” Obama said, mentioning the law’s promises of putting quality teachers in every classroom, establishing higher standards for learning, requiring accountability and highlighting achievement gaps among students.

“That’s the right thing to do,” he said at an Arlington, Va., middle school. “But what hasn’t worked is denying teachers, schools and states what they need to meet these goals.”

That’s why the law needs to be rewritten, he said.

Instead of labeling more and more schools as “failing” under the law, he wants a more flexible system that focuses on preparing graduating students for college and career and he wants better assessments to understand whether kids are meeting that goal.

Proficiency in math and science will continue to be emphasized, Obama said, but he added that skills such as critical thinking and creativity are also important.

Obama also said he wants to see a better effort at preparing and supporting teachers, holding them accountable for student progress and not making excuses for the occasional bad teachers.