Algorithm visualization (AV) software graphically illustrates how computer algorithms work. While the software initially had much promise as a pedagogical aid, research studies designed to substantiate its pedagogical benefits have yielded markedly mixed results. I argue that to harness the pedagogical promise of AV software, we need to rethink the theory of effectiveness that has guided its design and pedagogical use. My starting point is an alternative theoretical foundation that views learning not at the level of the individual, but rather at the level of the community of practice. On this alternative view, learning is seen in terms of participating more centrally in the practices of the community. To tailor this theoretical perspective to the particulars of the community of practice in which algorithms learning takes place, I conducted an ethnographic study of an undergraduate algorithms course in which AV software was used to facilitate students' more central participation in the community. Specifically, students were asked to use AV software to construct and present their own visualizations-two activities commonly performed only by community experts (algorithms instructors). The key finding of the study is that requiring students to use conventional AV software in this way actually impedes learning within the community, because it requires students to put inordinate amounts of time into community-irrelevant activities, and because it discourages students and instructors from engaging in meaningful conversations about algorithms. On the other hand, asking students to construct and present homemade visualizations made out of simple art supplies appears to avoid these problems. To explore this fmding further, this dissertation pursues two parallel research directions: (I) a controlled experiment that tests the hypothesis that, on a test of procedural understanding and recall, students who construct their own, homemade visualizations will outperform students who interact with a visualization constructed by an expert; and (2) a prototype AV system that supports the construction and presentation of unpolished, pen-and-paper visualizations. This research provides the beginnings of an alternative theory of effectiveness, which emphasizes the importance of students' constructing and discussing unpolished, pen •and-paper visualizations as a means of participating in a community of practice.