failing a class and retaking it

Depends

My school only takes the highest grade.

Really depends on the school. If they have a policy of letting people retake classes and taking the highest grade they will do that. The school I am going to apply to lets people retake prerequisites but they average the two grades together.

I agree with these guys- each school has their own policy. You can always call and ask, or attend an info session if they offer one. Some schools will average the grades, some take the highest, some won't take repeats, or will only take a certain number of them, etc.

one school in my town took the highest grade but another of them averaged the two grades and thats what you got

I can tell you with almost sure certainty that it is much better to re-take a class that you did not do well in (i.e., a C-). Administrators will like if you, for example, later received an A because that would mean that you understood the information much better than you did the first time. Of course, having an excellent grade the first time is choice. Plus, making a better grade will most likely raise your GPA (check their policy). It doesn't matter what school you attend, just as long as the school allows you to re-take a class if you desire. Failing a course is never appealing at any school.

It's all about each program's requirements. If you got a C in Micro in my local Community College District, they consider that you've passed the course and you're not allowed to retake the course in the District for a better grade. The RN programs will accept courses from other Colleges that are equivalent for a higher grade, but they prefer only one repeated course, but even that's individually evaluated. They do not have any recency requirements, so if you did repeat a prerequisite course after several years, they'd take that into consideration, because they know that some information isn't as fresh after a few years.