American here, after age 10, I grew up fairly poor and very rural. Within a half hour drive (on highways) from the home I grew up in, all the jobs were either in farming/agriculture, similar industrial (quarries or steel factory), grocery stores or gas stations.

The notion of going to college was virtually inconceivable to me and I was pretty sure I'd end up out in a field or a factory someplace. For a while I did odd manual labor jobs, sanding decks, cleaning gutters, digging drainage trenches, that sort of thing. My parents were simply unable to pay for any amount of college for me and I was barely making enough money to cover the gas and meals to get to and from and work at the various job sites. Coming out of that kind of environment, with no hope of ever getting to college, I didn't even bother taking the SATs in high school and barely graduated at all, nobody hiring farm work cares about your GPA.

Through a friend I managed to land a low-end tech job, but it provided me with just enough to pay for community college with lots of financial aid (I couldn't take loans because I wasn't sure if I could even pay them back).

Eventually, just because I was currently in college in a desirable field, I landed a paid internship that paid 3x what I was then currently making. I graduated, transferred to the local state school, converted the internship into a part-time job that paid even more.

At the local state school, I didn't make enough to pay for college and live, so I qualified for a number of grants which provided 100% of my tuition (I still had to pay for books and various other fees). Today the grants are about the same amount of money, but the state school fees back then were about 1/3 less than they are today thanks to generous subsidies, so I definitely benefited from that subsidy program. I couldn't have gone to my final two years of my undergrad in today's environment.

Because I was nearing the end of my undergrad, I was able to land another, higher paying internship with a performance-based conversion to full-time employment. When I graduated college, I converted to full-time and immediately doubled my income and started on a long and interesting career path.

Eventually I went back to grad school and got a Masters, which has again accelerated my career development.

So did I experience social mobility from cheap education fees? Absolutely. I think the most important thing is that had I not gone to college and ended up in dead-end farm work, the amount of taxes I would have payed back into the state would have been a tiny tiny fraction of what I've paid back since then. I've easily bought back the subsidies and grants used for my education several times over just in the tax difference that I've paid personally, and the additional economic benefits I'm able to provide working in my field far outstrip even that. For example, I've been able to hire people from out of state and out of the country and bring them into my state where they're now paying taxes back into the system.

It seems like such a virtuous cycle that I can't imagine why at least the levels of subsidies that I enjoyed haven't been maintained. It seems like such an obvious investment.