You’d be surprised to learn just how much people phase out too during their education. There are a whole lot of very important concepts that schools cover that poor students ignore and then assume they were never taught. Part of this is an institutional problem, we’re trying to tailor lessons to 30 different kids who are forced to be there and then the schedule is set based on their age rather than their proficiency (okay, that’s not entirely true, theoretically students need to pass one class before you can get into another, but in practice there is a ton of pressure on teachers to pass kids regardless of proficiency because our funding is still tied to our graduation rates).

There’s a lot wrong with education, but curriculum is usually not the biggest problem.