This paper examines students' mixed perceptions of the use of active learning techniques in undergraduate science lectures. Written comments from over 250 students offered an in-depth view of why students perceive these techniques as helping or hindering their learning and experience. Fourth- and fifth-year students were more likely to view in-class active learning techniques as a waste of lecture time, whereas third-year students and females perceived these techniques as instrumental to improving their understanding and their interactions with professors and peers. Students also provided recommendations for the effective use of active learning techniques in lecture. (Contains 1 table and 3 figures.)