This study examined the extent to which teaching practices and teaching experience predict mathematics skills of children's in the third through fifth grade by focusing on three cognitive components: (1) knowing facts and procedures, (2) applying this knowledge and (3) using reasoning. This study was longitudinal. The data was collected from 1,810 students and 90 teachers attending Estonian- and Russian-speaking schools. The students' were tested twice, at the beginning of the third and at the beginning of the fifth grade. The teachers were asked to complete a questionnaire assessing their teaching practices. The results revealed that teachers from Estonian-speaking and Russian-speaking schools' classrooms differed in their use of teaching practices and teaching experience. Teachers in Russian-speaking schools were slightly more experienced, and they reported using more teacher-centred practices compared to teachers in Estonian-speaking schools. The study showed different effects on the outcomes of the children attending classrooms where the study language was Estonian and Russian in solving arithmetic word problems when accounting for the teachers' use of different learner-centred teaching practices in the classroom.