This study was carried out to explore the verbal interaction between the teacher and students during teaching and its relation with students' academic achievement in primary schools. To this end, using multistage sampling, 400 teachers were randomly sampled from an original pool of 1600 primary school teachers in Ardabil. The students of these teachers totaling 10831 were asked to participate in the study. Flanders Interaction Analysis Categories System (FIACS) and documents were used for data collection ( the average score of every single students over one semester was used as an index of academic achievement and the number of codes registered for each factor of Flanders system was used as the predictor variable). Using Scott's formula, inter-rater reliability was calculated to be 0.81. Data were collected through observation. The study was correlational. The data collected were analyzed through multiple regression. The findings of the study can be summarized as follows: The greater part of classroom interaction centered on the teacher's lecture, whereas interactions concerning the under standing and appreciation of student's feelings were minimal. A positive correlation was observed between the teacher-students verbal interaction and the academic achievement of primary school students (P<0.01).