I remember giving better ratings to teachers of courses that were inherently interesting.
Even biases that fall outside traditional categories of discrimination — such as student negativity toward classes they perceive as overly challenging or taxing — harm an institution’s ability to use student evaluations to gauge instructors’ effectiveness. Professors who are perceived to be difficult, or who teach difficult material, may receive lower evaluations despite students’ often having greater success in later courses based on what they learned from those professors, as one study found.
Needull in a haystack 