There are two things every parent knows about preschool: They can’t live without it, and they can’t afford it. School systems around the country are now realizing the social damage wrought by that contradiction, and they’re rushing to invest in kids early, before it’s too late.

Early-childhood education, as a concept, is an easy sell politically. High-quality early-childhood programs are a key tool for improving children’s social and academic development, and are at least a step toward offsetting the impacts of income inequality and community segregation. Building on flagship programs like the federal Head Start system, many cities are expanding pre-kindergarten in scale and scope, to become a fully integrated facet of K-12 education, not just a place to park your kids during work.

Fewer than 25 percent of 4-year-olds nationwide has access to high-quality early-childhood education programs today, however. And despite major investment in preschool programs in recent years, cities have often overpromised on access and underperformed on quality, according to an analysis of programs in 40 major cities by the National Institute for Early Education Research (NIEER). The study suggests that if cities want to maximize pre-K’s potential, schools and providers need more funding, stronger staffing standards, and closer oversight of how pre-K is serving the communities most in need.

Researchers found that few of the country’s largest cities met NIEER’s core benchmarks for high-quality early education, based on criteria like training for teachers and professional educational development, systematic tracking of educational progress, and providing children with on-site health screenings. Although about half of the surveyed cities, including New York, Chicago, Boston, Houston, and San Francisco, have launched extensive pre-K-expansion initiatives, fewer than one in three of the 40 programs had a coverage rate of at least 30 percent of all 4-year-olds, and many school systems could guarantee access for just a fraction of preschool-age kids. Career opportunities for teachers were also lackluster; just 38 percent had a guaranteed requirement that “all teachers be paid comparably to those in the K-12 system.” The teachers also carried uneven burdens: Only half of the programs met the researchers’ minimal benchmark for class size of just one teaching assistant per 20 students. Educators also lacked opportunities to build skills and advance their career path, with just six of the 40 programs requiring professional-development trainings. Although specialized training for educators in areas like English-language learning and special needs can mitigate the impacts of poverty, professional-development programs in early-childhood education have generally been inconsistent in quality and funding.

The findings reflect the local implications of state-level gaps in early-childhood education investment; an earlier NIEER report revealed that across the country, many state governments were lagging in instituting comprehensive standards for preschool curriculum and teaching.

With many families unable to afford childcare programs—which typically cost $9,000 a year—preschool is an economic-justice issue not just for children growing up in disadvantaged communities, but also for the teaching workforce that serves them. Research has shown that quality early-childhood education is most effective when coupled with fair compensation and professional support, particularly since preschool staff generally earn much less than their K12 counterparts. The lack of in-depth training, peer support, and coaching programs exacerbates poor working conditions and contribute to a more precarious workforce. Nationwide, about 3/4 of early-childhood education teachers—who are disproportionately women, immigrants, and people of color—earn less than $15 per hour.

According to the University of California–Berkeley’s Center for the Study of Child Care Employment (CSCCE), high teacher turnover costs the public about $4 to $7 billion annually. The money that goes into replacing staff members who, as often happens, burn out or quit only aggravates the equity gap. since the most under-resourced programs get hit with “the highest turnover and replacement costs due to their higher rates of teacher departure.”

All types of families struggle to afford childcare, from working-class single mothers to two-parent professional households, but, with limited funding, cities face the perennial tension between access and quality. So while pre-K-for-all is an increasingly popular concept, many jurisdictions have a long way to go. Just a handful of cities, such as New York, have taken on the long-term agenda of investing in both access and quality. Some have used creative funding streams like the tax on sugary drinks in Philadelphia. In many cases, cities might seek to provide high-quality programs with a limited eligibility pool, or to invest less in programming per child in order to cover a larger population. NIEER estimates that based on current levels of program growth, “it would take 150 years to reach 75 percent enrollment, and much of that Pre-K provision would not meet the quality benchmarks necessary to create long-term benefits.”

At the same time, many cities are trying to expand preschool programs while strengthening quality. New York City; Washington, DC; Boston; and San Francisco have launched “3K” programs to incorporate 3-year-olds into the pre-K infrastructure. New York’s 3K pilot program in targeted low-income neighborhoods aims to incorporate many home-based childcare centers, which, unlike school- and center-based preschool settings, involve a more informal workforce of contractors who are paid through welfare-based childcare subsidies. Marcy Whitebook of the CSCCE points out that home-based childcare providers typically “have a contract, but they don’t have a regular salary, because they’re ‘self-contained businesses,’” which has historically resulted in lower wages and less-stable employment. So bringing more home-based providers into the city’s formal early-childhood-education system could be an opportunity to raise standards and compensation for home-based care. On the other hand, it remains to be seen what effect it could have on another goal of preschool expansion: mitigating structural segregation across the public education system. Researcher Kendra Hurley of the Center for New York City Affairs at the New School points out that home-based childcare is actually more segregated than the regular K12 system, so, for now, the current level of investment in home-based childcare providers is “unlikely to help integrate early education.”

Pre-K expansion could help address many of the more pernicious gaps in urban school systems, but only with the right blend of expanding coverage and workforce investment. When cities let their ambitions run ahead of their budgets, the most vulnerable kids get left behind.