We hold tightly to the idea of a public education system in the United States because while rich kids have been getting an education forever, poor kids have historically remained uneducated. Americans think of the public education system as the insurance that we truly live in a meritocracy where hard-working kids can rise above their family’s socioeconomic stature.

Behind this idea is a truth that doesn’t measure up. In the 1800’s you could come to America as a poor immigrant and make your way to the top. But around the same time we implemented compulsory education, we had a massive stagnation in social mobility.

Presumably, educators realize this, because it is well established that it doesn’t matter what sort of school you go to—good or bad, rich or poor—you will end up in the same social strata that your parents are in.

I had always thought that educators were trying to figure out what sort of education reform could overcome this stagnation. But then I read something stunning in Fast Company’s series on the death of the American Dream: No one knows why social mobility in the US is so bad.

We know why there is relative economic equality in smaller countries like Sweden and Denmark: homogenous, tiny countries are easier to govern. But we don’t know why Canada, a country that is similar to the US, has a much more financially fluid society.

Bhash Mazumder, a senior economist at the Federal Reserve Bank of Chicago says, “Why is the U.S. less mobile? I don’t think we really know with any great definitiveness what are the reasons of cross-country difference. That’s sort of an active area of debate.”

We have no idea what is causing the lack of social mobility in the US, yet we are spending billions of dollars to solve it with school. It’s an impossible situation. You have to know the cause of a problem in order to solve it. In the meantime, since we don’t know how to raise kids out of poverty, we should use public school as a way to make their life in poverty more livable. There should be fun and play and friends instead of school and homework and rules.

We have no evidence that school makes their adult life better, so we should at least use school to make childhood more fun.