There are financial and practical limits, as suggested above, but there is so much more government can do to create equality of opportunity that would, in my opinion, greatly improve our society.
In some democracies in Western Europe, and indeed, in many countries around the developed world, college is paid for by the state, and in full. This means from a very young age, everyone has the ability to attend university regardless of financial status. This means students could take more challenging classes, and would conceivably work harder to preapre themselves. The whole education system is improved in one fell swoop.
What's more, most economists will tell you that it's cost effective to do this, as college graduates earn much, much more over a lifetime, and therefore pay more in taxes on those earnings, essentially paying back government and society for the initial investment.