This meta-analysis reviewed inquiry-based science teaching studies from 1996-2006 to analyze their effectiveness. 58 studies were identified through searches of ERIC and Web of Science databases and coded based on levels of guidance and cognitive engagement. The analysis found that inquiry-based teaching had a positive effect on student learning, particularly when students engaged in exploratory and combined exploratory/conceptual activities. Studies with teacher-led guidance also saw higher effect sizes than less guided approaches. The study calls for refined models of instructional approaches and terminology standardization in science education research.