Science education reforms worldwide call on teachers to engage students in investigative approaches to instruction, like inquiry. Studies of teacher self-reported enactment indicate that inquiry is used frequently in the classroom, suggesting a high level of proficiency with inquiry that would be amenable to inquiry reform. However, it is unclear whether the high frequency of self-report is based on sound knowledge inquiry. In the absence of sound knowledge, high rates of self-reported enactment would be suspect. We conducted a study to measure teachers' knowledge of inquiry as it related to the known, high frequency of reported enactment. We developed a multidimensional survey instrument using US reform documents and administered it to 149 K-12 teachers at a national science teachers' conference. The majority of the teachers surveyed did not report inquiry enactment based on well-structured knowledge of inquiry. Interviews with participants showed how teachers could readily map non-inquiry activities onto inquiry statements taken directly from reform documents. From these results we argue that teachers often believed they were enacting inquiry, when likely they were not. We further reason that teachers may struggle to interpret and enact inquiry-related requirements of science education reform and will need support distinguishing inquiry from non-inquiry practices.