DISCUSSION

3.5 Did the increase in task completion cause the increase in performance?
So far we have shown that task-based goals increased the level of task completion and improved
student performance, with larger effects for male students than for females. A natural explanation
for our results is that the increase in task completion induced by task-based goal setting
caused the improvement in student performance. A final round of analysis provides independent
evidence that supports this explanation. In particular, if the effect of goal setting on performance
was caused by the increase in task completion, then this performance effect of goal setting
should be comparable in magnitude to the effect of goal setting on the number of practice exams
completed multiplied by the effect of completing a practice exam on performance. We show that
this is the case by estimating the performance effect of completing a practice exam using a fixed
effects estimation strategy. This strategy leverages within-student variation in the number of
practice exams completed across the two midterms and the final exam among students in the
Control group in the task-based goals experiment (who were not asked to set goals).
In more detail, we estimate the performance effect of completing a practice exam using a
fixed effects regression of points scored in one of the midterms or the final exam (which enters
the total points score as described in Section 2.4) on the number of practice exams completed
in preparation for that midterm or final exam. Each student-exam pair is an observation and
we include a fixed effect for each student. The estimation sample includes only students from
the Control group of the task-based goals experiment. Thus the fixed effects estimate measures
the performance returns to practice exams for students in the Control group who varied the
number of practice exams that they completed across the different exams (the vast majority did
so). Since students in the Control group were not asked to set goals, we estimate the effect of
completing a practice exam uncontaminated by any effects of our goal-setting intervention.
The fixed effects estimates reported in Table 7 suggest that completing a practice exam
increased the performance of students in the Control group by 1.486 points. If we multiply
this estimate by the effect of goal setting on the number of practice exams completed (0.491
exams, from the first column of Table 4), we predict an effect of goal setting on performance
of 0.730 points. This is remarkably close to the effect of goal setting on performance that we
estimated previously from a treatment-control comparison of the students in the task-based
goals experiment (0.742 points, from the first column of Panel I of Table 6). The equivalent
calculations using our estimates for male students and for female students also line up reasonably
well: for males the predicted performance effect of task-based goal setting is 1.241 points (1.389×
0.893) versus an estimated effect of 1.787 points, while for female students the predicted effect
of task-based goal setting is 0.247 points (1.579 × 0.156) versus an estimated effect of -0.128
points. Overall, our fixed effects estimates of the performance returns to completing practice
exams support the hypothesis that the increase in task completion induced by task-based goal
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