Seeing Program Output Improves Novice Learning Gains

In this article, we report results from a randomized controlled trial where novice programmers completed code mimicking exercises -- writing and modifying code shown to them -- designed to help learn the basics of how variables work. Using a tailored code writing system with feedback on program correctness, we conducted a two-group design study where only one of the groups could see the program output and feedback on the correctness of the program they wrote, while the other group just saw feedback on correctness. Learning gain was measured using a code-reading multiple choice questionnaire as both a pretest and a posttest. Our data suggests that being able to see program output leads to higher learning gains for novices, when compared to just being able to see feedback on the correctness of the code. For more experienced students, we observed benefits from code mimicking in both groups, without a strong distinction between being able to see the output and not being able to see the output. Based on our experiment, we recommend that environments used by novices for learning programming should encourage -- or even require -- running the code before allowing submitting the program for assessment.