CATNIP: An Automated Hint Generation Tool for Scratch.

Taking the first steps when learning how to program can be hard. Block-based programming languages like Scratch lower this hurdle, but learners may nevertheless get stuck when trying to solve a specific task and need help. This can also challenge teachers when facing many raised hands at the same time in the classroom. Consequently, it is desirable for learners and teachers alike to have access to systems that automatically generate hints on which steps to take next in a programming assignment. In this paper we introduce Catnip, a tool that generates next step hints for the Scratch programming language based on a structural comparison between model solutions and the current student attempt. Catnip uses extensive postprocessing to improve the generated hints, and displays them directly inside the Scratch framework, suggesting where to add or reorder blocks while working on a programming task.