Can we learn about users' problem-solving strategies by observing their actions? This article introduces a data mining system that extracts complex behavioral patterns from logged user actions to discover users' high-level strategies. Our application domain is an HCI study aimed at revealing users' strategies in an end-user debugging task and understanding how the strategies relate to gender and to success. We cast this problem as a sequential pattern discovery problem, where user strategies are manifested as sequential behavior patterns. Problematically, we found that the patterns discovered by standard data mining algorithms were difficult to interpret and provided limited information about high-level strategies. To help interpret the patterns as strategies, we examined multiple ways of clustering the patterns into meaningful groups. This collectively led to interesting findings about users' behavior in terms of both gender differences and debugging success. These common behavioral patterns were novel HCI findings about differences in males' and females' behavior with software, and were verified by a parallel study with an independent data set on strategies. As a research endeavor into the interpretability issues faced by data mining techniques, our work also highlights important research directions for making data mining more accessible to non-data-mining experts.