A statistics professor tests her students' level of knowledge at the beginning of the semester, and administers the same test at the end of the semester. She compares the two sets of continuous scores. Her research question is: Is there a difference in statistics knowledge from the beginning to the end of the semester? What is the appropriate statistic to address the research question, if the scores are not normally distributed?

Pearson Chi square (x2, Friedman test, or Wilcoxon signed-ranks test?