In this paper we describe initial findings from the development of a web-based learning environment aimed at teaching a systematic approach to debugging, meaning it supports learners’ identification and correction of errors in source code. During the use of the tool, learners iteratively narrow down the error space and subsequently explicate their experience knowledge in their personal logbook. The instructional design of the tool follows the Cognitive Apprenticeship approach. In order to explore learners’ behaviour and their first experiences with the tool, the think aloud protocol was applied with six undergraduate computer science students. The findings show a positive response to the systematization of the debugging process and indicate specific design actions that could be taken into account in order to further improve the tool.