CodeTree: A System for Learnersourcing Subgoal Hierarchies in Code Examples

Subgoal-labeled code examples help learners understand code patterns and apply them to different problem contexts. Subgoal labels are multi-level in nature and based on goal structures that define the hierarchical functional units in code. Data-driven methods and experts can supply the goal structures, but they do not work in environments with scarce data and limited availability of experts. Previous research has shown that learnersourcing is effective for sourcing high-quality subgoal labels of given goal structures. We extend this research by learnersourcing goal structures themselves, thereby making the generation of subgoal-labeled materials fully learner-driven. We introduce CodeTree, a system that generates multi-level goal structures by aggregating learner-generated subgoals from two subgoal learning activities---Generation and Selection. In a between-subjects study, 45 novices studied three code examples with either CodeTree or code explanations alone. The results showed that CodeTree could learnersource high-quality goal structures and subgoal labels for all three examples with just five learners. Learners reported a significantly higher learning gain and satisfaction compared to the baseline.