Nationwide, the average yearly tuition at a private, non-profit college has more than doubled over the last 30 years.

Experts debate what has caused the price hikes at private schools. Some point to high demand—as a college degree became more necessary for economic success—and fancy amenities.

Others argue that growth in federal financial aid actually drives price increases, with colleges pegging their tuition to how much aid is available. That’s more likely to be true at for-profit colleges, which rely heavily on government funding.

Selective non-profit colleges can draw on their endowments to subsidize scholarships, so many students don’t pay the sticker price. Low-income applicants often aren’t aware that this type of aid is available to them at private schools, a phenomenon known as undermatching.

In recent years, as financial strains have led to closures among small liberal-arts colleges, some have tried to stand out by cutting their prices—including Mills College in Oakland, which slashed tuition from $44,765 to $28,765 in 2017, saying it wanted to be more accessible.