President Obama’s call to “make high-quality preschool available to every child in America” seems like the right thing to do if you look at the research on the cost-effectiveness of the highest-quality preschool programs and the accumulating studies on the benefits of state pre-Kindergarten programs. Should every family in American have access to affordable, high-quality preschool? Of course they should. But policy commentators on the political right are raising questions about using federal money to pay for preschool, focusing their criticism on Head Start, the Great Society program targeted to low-income children that has produced disappointing results. However, Obama’s policy initiative is a good idea for several reasons and creates an historic opportunity to do something Head Start has not: broaden access to high-quality preschools for children from economically diverse families.

There is little argument that the results of the Head Start Impact Study, which began collecting data on children in 2002 and followed them through third grade, were underwhelming. Children were randomly assigned to Head Start, while others were not (and presumably enrolled in some other type of child care or preschool). Although Head Start modestly improved children’s preschool outcomes when compared to children who did “something else,” none of the benefits were detectable by the time the children reached third grade. This “fade-out,” or perhaps “catching up” of other children, has generated derision from Head Start’s opponents and consternation among its supporters.

While state pre-K programs have not been subject to such extensive scrutiny, several short-term studies suggest that they produce positive outcomes that are two or more times greater than those from Head Start. One possible reason is that the state programs are quite different from Head Start. Since its birth in 1965, Head Start has tried to boost the school readiness of low-income children by providing comprehensive services that include health and social services, as well as preschool education. Head Start tries to engage parents in their children’s development and devotes particular attention to children with special needs. In contrast to the “whole child” model of Head Start, state pre-K programs focus more narrowly on providing preschool education, with some states hiring only highly-educated teachers. In addition, several states have expanded program eligibility to families whose incomes are too high for Head Start, while other states allow children living in poverty to enroll in programs that also serve privately funded children. The two models, in many ways, are fundamentally different.

Knowing all this, Obama’s policy team wants to direct federal dollars to state pre-K programs, and encourage Head Start to concentrate its efforts more on serving families with younger children up to age three. Federal support for state-level pre-K programs would foster the experimentation required to determine which program components are critical elements of “quality,” and could help states build the systemic supports, such as early learning standards, data collection, and the use of assessments to improve instruction, for quality programs that the field has historically lacked.

Yet by expanding preschool access to families with moderate incomes, the Obama initiative also creates an historic opportunity to sharpen the policy focus on what constitutes high-quality preschool and to rethink Head Start. State pre-K programs have already been remarkably successful at offering access to economically diverse preschool classrooms, which Head Start, serving mostly families below the poverty line, cannot do. My own research, using data from 11 state pre-K programs, indicates that children who attend diverse pre-K classrooms learn more language and math skills than children in homogenous classrooms. On some outcomes, the benefit was comparable in size to the advantage of having a good (vs. average) teacher, and even rivaled the effect of children’s family background on how much they learned during a preschool year.

One might think the reason for this boost is that more diverse classrooms have better teachers than those serving high-poverty classrooms. But the data indicate that this was not the case, which suggests that what is really happening relates to positive peer effects. While the study was not randomized and therefore subject to the possibility that families in diverse programs nurtured their children’s learning in unmeasured ways, it is consistent with other research that has found benefits for children who attend preschool with peers who have more cognitive skills, at least as measured on assessments, which often correlates with higher income.

How could peers affect each other’s learning? In the best preschool programs, children engage in play that is rich in learning opportunities. They collaborate on projects and pretend together, often chatting expressively while constructing elaborate schemes and solving problems. In short, early learning occurs in a uniquely social context, which means children learn a lot from each other. In my own study and others on peer effects, no “harm” is done to higher skilled children, and they may benefit in unseen and even profound ways by forging friendships with children who are different from them.

To be fair, the founders of Head Start wanted an economically diverse program, but advocates for low- income families wanted to keep the programs focused on the least advantaged children. The President’s initiative creates an opportunity to revisit this question. It’s time to think about combining Head Start and pre-K programs that enroll four-year-olds, drawing on the strengths of both, to weave a seamless early education system. By offering preschool to more children who are living well above the poverty line, we could expand the number of economically diverse classrooms, and perhaps nurture more learning by children. That would be a better outcome for everyone.