Research stresses the importance of teacher sensitivity for the development of special needs students, including students with attachment problems. However, little is known about the antecedents of teacher sensitivity. This study investigated associations between teachers' daily negative emotions and teacher sensitivity towards individual students. Data were collected from 71 teacher-student dyads in special education primary schools and included students with mild to severe attachment problems (6 to 10 years old). Teachers reported their daily negative activating (e.g. anger) and deactivating (e.g. sadness) emotions in relation to individual students during a three-week period. Teacher sensitivity was observed in interaction with the target student in a cognitively challenging and an emotionally challenging task. Teachers' higher but decreasing negative activating emotions were associated with higher levels of observed teacher sensitivity in the cognitively challenging task. In addition, heightened levels of negative deactivating emotions were associated with lower levels of observed teacher sensitivity but only in the emotionally challenging task.