As an example, in the nordic countries where education is free, there quite effectively is nothing resembling a class system. Literally everyone with the mental and physical capacity is able to become e.g. a surgeon if they so choose. Correct me if I'm wrong, but in the US that's not really the case. You basically need either wealthy parents, a scholarship, or have to take massive risks by ending up with massive debt before you graduate, which means that if you don't immediately get a suitable job you're screwed. Also it's been said here that being born to a minority family in a poor neighborhood in effect blocks you from ever having a proper career.

I would think the former demonstrates income mobility better than the latter.