This is based on work that a visiting researcher presented at my university. I don't remember his name, but I could probably look it up.

He had data on individual student performance and their later earnings, which let him see the distribution of earnings within a class/major.

What he found was that only the top few students in each class had statistically significant returns from college and only in STEM fields.

For most of us this will probably ring fairly true, since we can think of who those top few students were in our own classes. They were probably super smart and hardworking, which makes it unsurprising that they went on to earn a ton of money. The rest of us more or less break even on college.