Many parents don't know when kids are behind in school. Are report cards telling enough?

Nearly nine out of 10 parents believe their child is performing at grade level despite standardized tests showing far fewer students are on track, according to a poll released Wednesday by Gallup and the nonprofit Learning Heroes.

- Annie Ma

Report cards, which many parents rely on for a sense of their children's progress--might be missing the whole picture researchers say. Without that knowledge, parents may not seek opportunities for extra support for their children.

"Grades are the holy grail," said Bibb Hubbard, founder and president of Learning Heroes. "They're the number one indicator that parents turn to to understand that their child is on grade level, yet a grade does not equal grade-level mastery. But nobody's told parents that."

In the Gallup survey, 88% of parents say their child is on grade level in reading, and 89% of parents believe their child is on grade level in math. But in a federal survey, school officials said half of all U.S. students started last school year behind grade level in at least one subject.