How does students’ knowledge of code structure improve as they progress through their degree? What are the areas where students struggle? We conducted a comparative study between CS1 and CS2 students to explore these questions. Using an online survey with several tasks, including identification the identification of expert patterns, judgment of readable structure, code comprehension, code writing, and editing, we focused on two important code structures: (S1) returning boolean expressions directly and (S2) unique vs.~repeated code within if and else. We found that student performance varied based on the code structures and tasks: in both S1 and S2, CS2 students demonstrated higher performance in identifying patterns, judgment of readable structure, and editing. However, evidence of improvement in code writing was only found for S1, and improvement in code comprehension was only found for S2. Therefore, students may need different supports across different code structures. With the exception of comprehension of S1, student performance was far below ceiling, suggesting that students need more support to attain proficiency in these skills.

Additionally, we examined how student performance in different tasks is related to their writing structure. Overall, there were limited and varying relationships between performance in other tasks and writing. Code editing predicted writing performance for both structures, while judgment of readability was also associated with writing performance for S1 and comprehension for S2.