WE had to do one every semester. It is very much like the boards but at the end it give you your score and it also prints out a grpah and a sheet telling you which subjects were average, above average, below average(what you need to work on). they aren't as scary as they sound and they are actually helpful(our teachers told us that the scores reflect what you would make if you took the NCLEX at that time) but don't get discouraged if the first one isn't the best. The test takes time to get used to(one of the reasons you do them) the NCLEX is very different from any other test and you have to practice!
~kelly