She also pointed out that the most well-known of these studies, the Perry Pre-School experiment, followed only 58 children. These kids received many benefits like parent counseling and home visits -- all bonuses that would certainly skew the results.
Libby Doggett, executive director of one of the leading universal preschool advocacy groups, Pre-K Now, defends the study because she believes it demonstrates the benefits of a massive investment in preschool for low-income children.
"Well that study was an incredible study because they did have a random assignment. They had children who didn't get this treatment and children that did get the treatment, and the treatment was really high-quality," she said.
And while that study concluded that preschool had a lasting effect on kids, plenty of other studies of the government's Head Start program point out that the gains from preschool tend to fade over time.
"By the second, third, fourth grade, they can't tell the difference between the kids that went to Head Start and the kids who didn't," Snell said.
In addition, studies have found that too much preschool may lead to kids becoming more disruptive and aggressive when they get to elementary school, a finding which Doggett acknowledges. But she insists that the government can provide high-quality programs that will avoid this problem.
"They're doing it in a number of states. Oklahoma is a good example. Georgia is a good example," she said.
It's true that those states have government-run preschool programs already. Oklahoma has had it for 10 years, and so has Georgia. They've spent billions of taxpayers' dollars on it, and the result? Not impressive. Oklahoma's performance has actually dropped relative to other states.
"We don't want to just focus on IQ scores," Doggett insists. "We want to look at how children are doing in their social and emotional, noncognitive development. ... Your children will learn more in pre-K than you could imagine."
But how can we be so sure that the government can do a high-quality job?
"This time, we're going to get it right," Lisa Snell said of the government's promise to American parents. "We can't get it right with Head Start, we can't get it right with K-12, but if you give us control of the preschool market in America, this time it will be high-quality."