The purpose of this paper is to examine the reasons behind teachers' negative attitudes about classroom observation. This multiple-case study interviewed five teachers from different private language schools in Iran. The themes emerging from in-depth interviews suggest that the negative attitudes could be related to the observer effect, teacher's performance anxiety, lack of external motivation, ambiguity of the purpose of observation, the hierarchical nature of teacher-supervisor relationship, job insecurity and lack of sense of belonging, disregarding the developmental level of the supervisee, accompanying observation with no other techniques, lack of teacher autonomy, improper quality, quantity, and frequency of the visits, improper quality and quantity of feedbacks, improper quality of communicating the feedback.