At the school I went to, if you were an undergrad, there were certain credit hour levels that constituted different tuition amounts. Fore example, 12 credit hours would cost $4,000, 15 would cost $5,000, and 19+ would cost $6,000 (these numbers are mostly made up but serve to demonstrate how it would work). Once you graduate and obtain a degree from that school, they then charge per credit hour, i.e. tuition is $500 per credit hour. If you took one class, this wasn't a big deal, but if you took a full 18 cr hour semester, the cost in this case would be $9,000, significantly more than the cost prior to graduating. Basically, many schools charge you graduate student rates once you graduate, regardless of if you actually are a grad student or not. This is why most SMPs and post-baccs cost so much money.