Republicans and conservatives have questioned the effectiveness of Head Start programs, citing studies such as a Health and Human Services Department report last year that showed that while at-risk students enrolled in the pre-kindergarten programs saw tremendous gains in vocabulary and social development, those benefits largely faded by the time students reached third grade.

The HHS report didn’t explain why the students saw a drop-off in performance or predict how they would fare as they aged. But it was a favorite reason to question Obama’s plan.

“There’s reason for huge skepticism,” said Mike Petrilli, the executive vice president of the Thomas B. Fordham Institute, a conservative education think tank. “Most states are still in a ditch financially, and it’s going to be a couple years before they’re out of it. … I don’t know where the states are going to come up with the money for this.”

Scores of other studies, however, were more favorable on the program, which has been shown to make at-risk students more likely to complete high school and avoid criminal arrests. In pure dollars and cents, academics called it a smart investment.

Advocates for more early childhood education said states already are working to help the most at-risk students and could be willing partners for Obama if it was worth leaders’ time.

“There is no way to work on the scale he’s describing without engaging with states and partnering with states,” said Kris Perry, executive director of the First Five Years Fund, which advocates early education programs for at-risk children. “He’s going to have to work on both sides of the aisle. He has the strength of great evidence but he’ll need help from everyone to get this through.”