Seventy percent of Americans want federally funded pre-kindergarten programs, according to a recent Gallup poll, but studies show that benefits may taper off over time and differ widely between socioeconomic groups.

The Gallup poll tracked those who supported President Obama’s goal to give every U.S. child a preschool education, and support crossed partisan lines. This pre-kindergarten push stems from the educational disparity between low-income students and their peers, according to Gallup.

The study found that most Democrats support this proposal and barely more than half of Republicans do, while only 52 percent of Democrats — and 34 percent of Republicans — view preschool as “extremely important.” But the difference isn’t there when it comes to income. Around 40 percent of all respondents saw preschool as “extremely important,” and that held true when broken down by income groups.

Gallup concluded that while Americans think preschool is an important investment, they think the basic K-12 program is more important.

So is preschool worth the money?

Research by the Society for Research in Child Development shows that preschool improves future test scores, but only up to a certain point.

“While there is clear evidence that preschool education boosts early learning for children from a range of backgrounds,” SRCD says, “we also see a convergence of test scores during the elementary school grades so that there are diminishing differences over time on tests of academic achievement between children who did and did not attend preschool.”

Even though test scores eventually even out between those who went to preschool and those who did not, SRCD says that preschool attendance correlates with higher educational attainment, a better income, fewer cases of teenage pregnancy and less criminal behavior.

But economics professor Elizabeth U. Cascio and social policy professor Diane Schanzenbach don’t entirely agree. Their research of state-funded pre-kindergarten in Georgia and Oklahoma shows that universal preschool improves the test scores of lower-income students but doesn’t impact their peers at all. However, they point out, that is likely because many higher-income students already go to preschool and just switch to the free programs when they become available.