This study examined similarities and differences in how U.S. and Japanese middle-school science teachers teach science through inquiry. Classroom practices were examined through observations in the United States (N = 9) and Japan (N = 14). The observational data were coded and quantified based on the rubric that incorporated 2 dimensions: student self-directedness and the depth of conceptual links. The conceptual link dimension measured how much cognitive scaffolds that teachers provided in order to help students construct conceptual understanding. A multivariate analysis with country as a factor variable was performed for 10 categories involved in the rubric. The results show that country has a significant main effect on the overall categories. The univariate analysis on each of the categories identified 4 specific areas in which U.S. and Japanese classroom practices differed significantly. The results show that little inquiry-based teaching was observed in either of the countries for apparently different reasons; the observational data indicate scientific concepts under the classroom discussion were not clearly identified in many of the U.S. lessons, whereas Japanese lessons often exhibited lack of teachers' support for students in constructing their own understanding of scientific concepts. Teacher interviews were also conducted to examine U.S. (N = 9) and Japanese (N = 15) teachers' definitions of inquiry-based teaching. The results show that the majority (79%) of teachers in the 2 countries thought that inquiry-based teaching includes student own explorations of scientific concepts. The findings imply that teacher beliefs on the importance of student self-directedness in inquiry-based teaching might be acting as an obstacle for increasing inquiry-based teaching both in the United States and Japan. Although the findings should be interpreted cautiously because of the small sample size, this study suggests critical elements that each of the countries might be missing for their implementation of inquiry-based teaching. (Contains 2 figures and 5 tables.)