A school has 415 third graders and 338 second graders. How many more third graders are there than second graders?
There are 415 - 338 = <<415-338=77>>77 more third graders than second graders. Answer: \boxed{77}.
To find how many more third graders there are than second graders, subtract the number of second graders from the number of third graders:
415 - 338 = 77
Therefore, there are 77 more third graders than second graders.