It depends on the school I'm sure, where I go to school you can, but there are some restrictions that I forgot. So far I have taken 2 classes over again and may well take a third. I think employers might might look, but what really matter (I hope) is that in the end you knew the subject. There was one class where I completely forgot we had a test and ended up getting a 40 on a grade that was 30% of the total (and this is in a class where the average was like 80, not one where the average is 50 and the grades get curved at the end). The other time was just a really hard class that I really had troubles with the first time around, but the second time it all made waaay more sense. I was fortunate to have a ton of AP credit going into college, so retaking classes doesn't really set me back in terms of graduating on time, but obviously if you don't have any AP credit it could really hurt to have to retake several classes.