Finding the two-humps and practice in APCS

January 14, 2010 at 10:49 am 5 comments

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.

via Practice and Performance « And Yet It Moves.

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.

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Flagship Universities Straying from their Mission The Future of SIGCSE

5 Comments Add your own

  • 1. Greg Wilson  |  January 14, 2010 at 12:25 pm

    How much of this result can be explained by the divide in your following post on universities straying from their mission ( I.e., is there correlation between pre-university income levels or other aspects of students’ backgrounds and their placement on the two-hump curve?

  • 2. Raymond Lister  |  January 14, 2010 at 3:55 pm

    Perhaps the people who had time to try the JavaBat problems were people with prior programming knowledge??? In general,
    when looking at notions of two-hunps, I think we have to remove
    the prior knowledge factor before thinking too hard about the humps.

    How about talking to a few of the higher performing students, to find out if they had prior programmming knowledge? You also might get from them some further ideas on what contributes to their success.

  • 3. Ben Chun  |  January 16, 2010 at 3:47 pm

    @Greg – This is a public high school population, and in general I couldn’t find any correlation between demographics and performance. (Looking at gender, ethnicity, or parent education levels.) The class demographics, however, do not match the school’s demographics, which in turn do not match the district’s demographics, all of which are troubling points.

    @Raymond – Of the top quartile, most (but not all) had some prior programming experience (and not all with me). That may indicate that prior exposure is helpful, or it may indicate that students who fail their prior experience chose not to take a second class in a subject they were unsuccessful with. Great idea to ask students about their experiences – I shall do that.

  • 4. More Performance Correlates « And Yet It Moves  |  January 16, 2010 at 4:16 pm

    […] Taking the intro class turns out to be worth about a letter grade (12%) on the average score. But it’s no guarantee that a student won’t fail, and not a prerequisite for success. Not all students from the intro class go on to this class. So it’s also quite possible that the first course merely serves as a filter for students who would fail, not as a transformative educational experience that ensures later success. I suspect reality might be somewhere between these extremes, but the camel still has two humps. […]

  • […] 4, 2011 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 […]


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