This is a good approach. Noone enjoys explaining face-to-face why they owe you money, and will probably do what they can to avoid this potentiallly embarrassing

This is a good approach. Noone enjoys explaining face-to-face why they owe you money, and will probably do what they can to avoid this potentiallly embarrassing phone call. If you come off as a really nice guy that really needs the money it'll help your case. You're a student and you don't have any money for the summer. i've noted over the years that the people you deal with mirror your mood. If you act as a nice guy they act nicely. If you send in a lawyer they'll send in their lawyer. If you scream and shout they'll do the same. And screaming and shouting gives an excuse to believe that you're an idiot and don't deserve the money anyway or if cash is the problem for the company that someone else is first in line. Act nicely but be firm. Make it clear that you're not going to go see your aunt Betty before she dies of lung cancer this summer if you don't get the money. (OK, maybe that's a little thick but you get the point) Make him feel guilty.