That school was a quarterly school with 4 credits per class, twice a week. A quarter is 12 weeks (I think).There are 3 3 month long quarters in a typical school.
The school I've transferred to is setup like this; - full time is 18 credits - anything over 21 credits is the same as above - part time is under 12
This school is on semesters, each class is usually 2.75-3 credits which is 2-3 times a week. A semester is 14 weeks (I think). There are 2 semesters in a year.
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In the summer, it's usually split in half with a week between them. Basically, you're doing twice the work in half the time of a normal semester/quarter. Some people like it better because of that and some don't really care much for it.
Thats a semester though, so double that for a year.