This September, millions of college students move to campus for their first semester. Many will begin courses in engineering, calculus, science, or another advanced field, but other incoming freshmen will be stuck in remedial classes, reviewing material they should have learned in the ninth or tenth grade.

According to a 2016 report from the Center for American Progress, a liberal think tank, somewhere between 40 to 60 percent of first-year college students now require remedial courses in math, English, or both. This means that millions of students across the country are trapped in classes that only cover content they should have learned in high school.

The prevalence of remedial college courses represents an obvious failing of our K-12 public school system. Increasing school choice could be a solution.

After all, it’s clear that traditional public schools simply aren’t working. Americans spend around $12,000 per student annually, nearly 30 percent more on average than the other nations in the Organization for Economic Cooperation and Development (OECD), a group of 35 developed countries, yet U.S. students rank 30th in math and 19th in science.

Would dumping more money into public schools bring about better results? Unfortunately, no. The conservative Heritage Foundation measured both spending-per-pupil and academic accomplishment from 1970 to 2004, and found that while per-student spending nearly doubled, reading proficiency scores stayed flat.

Additionally, high school graduation rates have remained fairly consistent since the 1990s, despite increased education spending. At the very least, it’s clear that increased taxpayer outlays are no surefire solution to America’s academic woes. So if we truly want to start preparing students for college, we need to offer them opportunities away from our broken public K-12 school system.

The best way to do that is through school choice programs, which give families the opportunity to choose the best school for their children by providing alternate options, such as publicly funded charter schools and granting families taxpayer dollars to cover private school tuition.

The American Federation for Children (AFC) is one of the largest school choice advocacy organizations in the country. I spoke with AFC President John Schilling, and he told me that “the more opportunities that you give families to choose the best K-12 educational environment for their child, the better these students are going to do in college.”

There’s quite a bit of empirical evidence to back up his claims that school choice could improve outcomes on campus. According to AFC documents, “17 empirical studies examined academic outcomes for students participating in private school choice using random assignment, the ‘gold standard’ of defensible social science: 11 report positive test score effects, and only 2 report negative impact.”

Standardized test scores closely correlate to first-year college GPA, so if school choice can help raise students’ scores, it can help them succeed on campus too—and, hopefully, lower the ever-increasing need for remedial courses.

Data obtained from AFC also reports that school choice programs in Florida increased college enrollment by 15 percent, while high school vouchers in Milwaukee increased college matriculation rates by 9 percent. Programs in Washington D.C. led to higher high school graduation rates and reading scores. In all three programs, many of these gains went to low-income students, who are often members of minority groups. Such impressive results for society’s disadvantaged youth should win support for school choice among progressives.

Yet critics on the Left insist that school choice programs, particularly those involving private vouchers, divert crucial money away from supposedly cash-strapped public schools, leaving the students that remain enrolled even worse off. They also argue that private schools aren’t held to the same standards as their public counterparts.

While it’s true that school choice programs do redirect some money away from public schools, they also take students away. There’s no reason schools should keep the same funding when educating fewer students. As far as the notion that private schools are unregulated and unaccountable, the only true unaccountability lies in the absence of school choice, wherein parents have no option but to continue sending their children to a public school that doesn’t meet their child’s needs. Parents’ power to choose is apt to check private schools.

The question, then, remains: Why won’t the Left support school choice? When I asked Schilling, he gave me a two-word answer: “Teachers’ unions.” Public-school teachers unions give more than $30 million to Democrats every year, and unions oppose school choice because the status quo reinforces their power.

Public school teachers have historically been required to join teachers unions, leading to more union dues and thus power for the organizations. School choice programs shift more teaching jobs over to private schools, where teachers aren’t required to unionize, making the unions less powerful—giving them an obvious organizational incentive to lobby against school choice, regardless of what’s best for students.

Yet school choice does align with some of the Left’s other stated goals, like helping poor and minority students get a leg up. Of the 500,000 kids participating in voucher programs nationwide, nearly 400,000 are low-income or minority students, according to AFC. Additionally, minorities are the group most poorly served by our current public education system, and set up for the most challenges in higher education: that’s why 60 percent of black and Latino students at four-year colleges have to take remedial courses. Repeating classes puts minority college students at a disadvantage against their peers, adds extra costs, and drives down the likelihood that they’ll graduate on time. Shouldn’t Democrats want to avoid that?

While a few liberal politicians such as Sen. Dianne Feinstein (D-CA) and Sen. Cory Booker (D-NJ) have broken from their party and supported school choice, almost all of the larger school choice programs implemented nationwide were put in place by Republicans. If Democrats really want to help disadvantaged groups succeed in K-12 education and beyond, they should be willing to break away from party orthodoxy to support education reform, even if means turning their back on teachers’ unions.

Regardless of how much teachers donate to campaigns, it’s unacceptable that our public K-12 system school is failing so miserably and leaving so many students poorly prepared for what comes next. Colleges are meant to prepare students for the workforce, but they can’t do that if students are showing up to campus already a step behind.