According to a recent US study, students think males are more knowledgeable than females when it comes to teaching physics.
Amy Bug, a (female) physicist at Swarthmore College, and her team trained four actors (two male and two female) to give a 10-minute, scripted physics lecture which was filmed. 126 real physics students were then shown a lecture by one of the four actors and their opinions surveyed.
On average, the male 'lecturers' received higher scores then the females. While female students gave slightly higher scores to female 'lecturers' male students rated male 'lecturers' vastly better.
When the students were asked if the 'lecturer' had a "solid grasp of the material", if they were knowledgeable, or good with equipment, there was a distinct gender bias with both male and female students rating the male 'lecturers' more highly.
However, when asked whether the 'lecturer' "teaches in a way that rally helps students learn", is well organised or interacts well with students, there was evidence of a distinct own-gender bias, with females rating female 'lecturers' most highly and males preferring male 'lecturers.
A note of caution is required here though: How do we know that the bias shown is not a result of the relative skills of the actors to play the part of a physics teacher?
You can view a report on the study here.
Scientific American look at this study in their 60-Second Science podcast.