Teaching by inquiry is touted for its potential to encourage students to reason scientifically. Yet, even when inquiry teaching is practiced, complexity of students' reasoning may be limited or unbalanced. We describe an analytic tool for recognizing when students are engaged in complex reasoning during inquiry teaching. Using classrooms that represented "best case scenarios" for inquiry teaching, we adapted and applied a matrix to categorize the complexity of students' reasoning. Our results revealed points when students' reasoning was quite complex and occasions when their reasoning was limited by the curriculum, instructional choices, or students' unprompted prescription. We propose that teachers use the matrix as a springboard for reflection and discussion that takes a sustained, critical view of inquiry teaching practice.