Students are often unable to collect the real-time data necessary for conducting inquiry in science classrooms. Web-based, real-time data could, therefore, offer a promising tool for conducting scientific inquiries within classroom environments. This study used a quasi-experimental research design to investigate the effects of inquiry-based instruction coupled with archived online data. Ninety-six preservice teachers in a four-year elementary science teacher-training program participated in this study. The students were enrolled in three sections of the methods course, and these existing groups were randomly assigned to the treatment groups: traditional instruction, traditional instruction supported with a simulation, and inquiry-based instruction with archived online data. Data were collected with structured interviews and analyzed with the constant comparative method and one-way ANOVA. Before the instructional interventions, none of the participants had a "scientific" understanding of tides, and 15% of the participants had "no conceptual understanding" of tides at all. After instruction, 72% of the participants who received inquiry-based instruction with archived online data were categorized as having scientific conceptual understandings; 46% of participants who received traditional instruction supported with a simulation were categorized as having "scientific" conceptual understandings; and 43% of participants who received traditional instruction were categorized as having "scientific" conceptual understandings. Statistical analyses showed that the group receiving inquiry-based instruction with archived online data performed significantly better than the other two instructional groups. Inquiry-based instruction with archived online data can be used to effectively perform inquiry activities within science classes; it might be used at different grade levels to teach a variety of scientific content. (Contains 6 tables and 4 figures.)