In a world in high demand of engineering professionals, higher education should be effective and quality conscious. A better understanding of what type of activities that are best suited for improving students' learning could enable further improvements. In this paper, the effect of mandatory assignments on students' learning outcome in introductory programming courses is explored through a quasi-experimental research study. One group of students were exempted from the mandatory weekly assignments and followed up via biweekly sessions. A control group was recruited to follow an assignment regime in parallel. Through pre-and posttests the learning outcome of the two assignment structures was statistically evaluated. The results indicated that the group of students exempt from mandatory assignments achieved the same learning outcome as the control group. Similarly, no difference was found between the two groups on exam performance. Students have individual learning behaviors and learn to program in different ways, and the instructional design should facilitate individual learning trajectories.