Wikis are gaining popularity in classrooms because of their many benefits. Despite these benefits, there is a shortage of empirical data regarding their effectiveness in increasing knowledge. This study examined (a) the effectiveness of creating/developing/using a wiki to increase knowledge of Web 2.0 tools for 103 preservice teachers; (b) their perceptions of the use of a wiki to increase knowledge of Web 2.0 tools; (c) the frequency of use while participating in the reader, writer, and editor roles; and (d) their communication habits. The results revealed that there was a significant gain in achievement. Further, the preservice teachers reported that the wiki was effective for increasing their knowledge of Web 2.0 tools, and more than 75% used the wiki as an information source during and after the activity. The preservice teachers indicated that the creation of the wiki increased their knowledge as well as the presentations given by their peers, but the hands-on practice increased their knowledge the most. When examining preservice teachers' participation in the reader, writer, and editor roles, the results indicated that they read the information but were less regular in posting or modifying the wikis. Upon examination of the communication habits of the preservice teachers, the results indicated that they did not actively communicate with each other during the development stage of the study guide. They reported using email the least, comments within the wiki a little more, and face-to-face conversations the most. This study demonstrates that wikis can be used to increase knowledge. Additionally, the findings can serve as a guide to educators who want to use wikis as a teaching tool. (Contains 1 table.)