Teaching strategies are becoming increasingly oriented toward guiding students' knowledge construction through cooperative learning. Enhancing students' cognitive development is a priority; students must "learn how to think." Inquiry instruction provides students with tools to make decisions based upon available evidence and an opportunity to develop and practice their thinking skills. Inquiry-oriented teaching strategies are significantly better than traditional instructional methods for increasing reasoning ability (McKinnon and Renner 1971). The learning cycle (Lawson, Abraham, and Renner 1989) is a five-phase model of instruction that includes engagement, exploration, explanation, elaboration, and evaluation (Trowbridge and Bybee 1990). The learning cycle application described in this article is an inquiry unit on gas laws, suitable for high school chemistry or physics, which focuses on the explanation phase of the cycle where students begin "making sense of the data." In this investigation, students construct their own conceptual understanding of absolute temperature, Charles's law, and Boyle's law. In contrast to a traditional inform-and-verify approach, this unit follows a data-to-concepts sequence where students are guided toward the concepts with peer leader and teacher assistance. By participating in this type of inquiry-oriented curriculum, students are learning how to form and test hypotheses from available evidence. In addition, students are not being told what to think, they are learning how to think. (Contains 2 tables and 4 figures.)