[tptacek]

Part of the problem here is that the allocator doesn't need to know how big the crap the pointer is pointing at is; it only needs to know that the crap is smaller thank the chunk it allocated.

If you're going to teach people something unorthodox about C programming, writing custom allocators would probably be a great one. In more than one job I've crushed optimization problems on code written by people way smarter than me simply by knowing to profile allocation and replace malloc.