Creating explanations is an important process for students, not only to make connections between novel information and background knowledge, but also to be able to communicate their understanding of any given topic. This article explores students' explanations in the context of computational science and engineering, an important interdisciplinary field that enables scientists and engineers to solve complex problems. Specifically, this study explores: (a) students' approaches to create written explanations of programing code and (b) the relationship between students' explanations and their ability to do computer programing. Students wrote in-code comments for 3 MATLAB® worked-examples, which were qualitatively analyzed using a coding scheme. Different approaches to self-explain were identified using hierarchical cluster analysis, and differences in students' ability to do computer programing were identified using analysis of variance. The resulting approaches to self-explain were: original solution, mechanistic, principle-based, limited, and goal-based. The findings suggest that experienced students wrote simple in-code comments to self-explain, but students with lower ability to do computer programing wrote more comprehensive explanations, as they may take this as a learning opportunity.