One of the most impressive phenomena in the creation and dissemination of human knowledge in recent years is Wikipedia, an encyclopedia written collaboratively by Web users. Nevertheless, teachers tend to oppose the use of Wikipedia by their students and question its reliability. This paper explores the perceptions of k-12 school teachers in Israel towards the quality of the information in Wikipedia and the reasoning they hold for these perceptions. Findings show that most of the teachers perceive Wikipedia as an environment of middling to poor reliability, accuracy, and timeliness. Many teachers do not realize how authoritative information is when generated by "wisdom of crowds" and interpret it as unacceptable and untrustworthy.