Archive for January 4, 2011

Enormous variance from one CS class to the next

Last year, I did a blog post referencing Ben Chun’s analysis of his APCS class. He just re-did the analysis, and didn’t find the same significant correlations that he did last time.  That’s quite interesting, and points to the enormous variance that we see from one CS class to the next.

A wise math teacher, Henri Piccoto, quotes Tofu Roshi: “There is no one way.” I’m reviewing this line of thought because I just finished grading the final exams for my AP Computer Science class. Last year, I had strong indications that students who did more independent programming practice did better on my exam and subsequently on the AP test.

This year, that same correlation really isn’t there. Many things are different, including my sharing the previous data with this year’s students and some changes to the exam.  Most significantly, these are just different humans, each coming in with their own mental models and skill sets.

Last year, the correlation with CodingBat completion was r = 0.71. This year, r = 0.18. So maybe doing some amount of those exercises matters for some students. Maybe not. Last year, when I looked at the correlation with CST Math scores, I found r = 0.49. This year, r = 0.64.