Background and Context. Misconceptions in programming have been studied extensively, but most research focuses on uncovering and assessing misconceptions in students. When teachers are involved, it is usually only to elicit their perspective on misconceptions in their students. However, there is no guarantee that teachers do not hold misconceptions themselves. Detecting the possible presence of misconceptions in teachers is a crucial step for improving their content knowledge and pedagogical content knowledge, which benefits hundreds of students each year.

Objectives. The study aims to answer the following research questions: Which programming misconceptions do teachers themselves hold? Are teachers aware of these misconceptions, observe them in their students, and consider them important? Are there differences in the teachers’ perceptions, depending on whether they hold misconceptions themselves?

Method. We conducted an extensive, 55 pages long survey of high school CS teachers who teach programming in Python. The survey focused on 16 Python misconceptions reported in prior research that involve concepts covered in the teachers’ high school courses. The first part of the survey assessed whether the teachers held misconceptions, probing their knowledge with two related questions for each misconception and asking for mandatory explanations. The second part of the survey asked teachers whether they previously knew about the misconceptions, how prevalent they were in their students, and how important they believe them to be.

Findings. The number of teachers who gave incorrect answers on programming misconception questions varies considerably by misconception, ranging from 3% to 40%. Most teachers report being familiar with the misconceptions that were part of the study, consider them rather important, and have observed them at least once in their students. Teachers who answered correctly consistently rate misconceptions as more important and more prevalent among their students.

Implications. When teachers hold misconceptions, all of their students can be affected. This study highlights the importance of professional development for teachers so that they can both correct their own misconceptions and recognize them in their students, ultimately leading to better programming education. Our results also caution computing education researchers against assuming that teachers are free from misconceptions. We recommend that future studies include an assessment of the participants’ knowledge, to ensure that findings are properly contextualized.