Erlang, just for fun:

  grade(#student{work=Work, tried_hard=Tried}) -> grade1(Work, Tried).
  grade1(excellent_work, _) -> 'a+';
  grade1(okay_stuff, yes) -> b;
  grade1(okay_stuff, _) -> 'b-';
  grade1(_, _) -> c.

Edit: formatting.