I have a set of 15 perception questions asked before and after a course to the same group of 13 students. The responses are 0%, 20%, 40%, 60%, 80% and 100%. What is the best way to analyze them to test for significant difference?
I would use the Wilcoxon signed-rank test. That test does not depend on the distribution type, that is, it is a nonparametric test. Thus, that the data categories are ordinal should make no difference as the ranking procedure is also ordinal.
Other questions you might want to answer include nonparametric significance of difference of variance for which I would use Conover's squared ranks test.