Finding the two-humps and practice in APCS
Ben Chun gave the same final exam to his 2008 and 2009 AP CS classes, and in so doing, found the two-hump observation in his result:
But the bell curve turned into a bathtub! Why? There are so many variables that it’s really hard to know. It’s worth noting that I’ve run the class through the material much faster this year, which probably exacerbates any spread between high and low performers.
What’s also interesting is his correlation with practice and performance.
But here’s something else I noticed: All of the top scoring students have also completed a significant number of optional practice problems using Nick Parlante’s excellent JavaBat. I introduce this tool at the start of the year and offer them extra credit for doing the problems. (To be clear: the extra credit is not part of the exam scores, so that’s not the proximate reason their scores are higher.) I found a strong positive correlation of r=0.71 between the number of practice problems completed and exam score.
Is there a geek gene explanation here? Is it that the top students became top students through the practice, or were the top students more inclined to practice — thus the practice wasn’t actually causation for the better performance? Not clear how to test to distinguish these conditions.