This study aims at identifying indicators of schoolteachers' professional development by learning teachers' perceptual and thinking capabilities of classroom events as reflected in their comments. The analysis of comments produced by novice and expert teachers on videotaped lesson activities, based mainly on the grounded theory strategy, revealed that expert teachers are more sensitive towards certain instructional events and to general teaching strategy used by the model teacher than novice teachers. The findings of this study might be useful for promoting student teachers' professional sensitivity towards relevant features of classroom instruction and atmosphere in pre-service teacher education programs.