Mayor de Blasio once promised to “shake the foundations of New York City education” and bring real change to failing schools.

That was in 2014. Three years later, the foundations remain unshaken and, in fact, the main question is where all the money went that was poured into his plan.

As reported in these pages last week, the city is spending $186.5 million a year on Renewal schools, or about $14,632 a pupil. Meanwhile, enrollment at these schools has plummeted 25 percent since the program began in 2013 and only three of the 72 schools met their achievement goals last year.

This is an abject failure. Instead of throwing good money after bad, schools need the freedom to experiment and tailor their curricula to the needs of their students.

PS 118, a relatively new school in Park Slope (it currently only goes to third grade) last year did away completely with homework. Word got out, and the school became one of the most popular in the five boroughs.

What’s particularly unusual about PS 118’s popularity is that it has yet to show any testing results to see whether the experiment is actually working.

State tests begin in third grade, so this will be the first year they are offered at 118. So why are parents lining up to make their kids guinea pigs at the school before the results are in? Because while test scores matter, they are far from the only metric parents use to assess the value of their children’s education.

Case in point: On the other end of the spectrum is PS 195 in Manhattan Beach. It’s also one of the most popular schools in the city yet parents report a significant amount of homework. Many of the kids are children of immigrants from the former Soviet Union, and one parent told me that “a large amount of homework is expected by these families as evidence of a good education.”

Choice in education is a good thing. When parents can choose which schools their kids attend, they’re more invested in the process than if they get funneled into a school that doesn’t fit them based on their address. But school choice should also mean that the schools have freedom — to make more of their own choices about how they will fit their student population.

Homework is only one example. But generally public schools don’t have a lot of room to maneuver, and that uniformity can stifle the creativity necessary to break the kids out of their educational malaise.

Last year, Schools Chancellor Carmen Fariña said, “If you are a [low-performing school in the “Renewal” program] or a school where you have struggling kids, you have less autonomy.” She added that we “need an equity system” and “you’re not going to have it if the principals in The Bronx can do certain things differently than the principals in Park Slope.”

That’s exactly backward. The failing schools might be failing because they’re emulating strategies that have worked elsewhere but don’t work for them. An equity system is more achievable when schools have the space to do what works for their individual student bodies.

One reason charter schools continue to gain in popularity is because of the flexibility they have to adjust to their student population. Our regular schools need more autonomy, too, to do what they need to do to help their students.

Education columnist Alina Adams has a son who goes to a charter school that has a policy to never close, even during snow storms, because that is what their students need to succeed in school.

In a column for New York School Talk, Adams writes: “When we talk about school choice, we tend to focus on academics, on rigor, on testing. But there are other issues in play as well. When we talk about school choice, we should be talking about absolutely everything that affects a child’s K-12 experience. And about leaving as many of those choices in the hands of parents (and later, yes, even the children) as possible.”

Fixing our schools requires taking the reins out of the hands of politicians and teachers unions and giving them to individual schools and communities. That’s in everyone’s interest — especially the students’.