Study aim: To evaluate verbal and non-verbal behaviour of teachers and pupils in elementary swimming education and their impact on pupils' achievements. Material and methods: A total of 77 swimming lessons were videorecorded and coded with the modified Cheffers' Adaptation of Flanders Interaction Analysis System (CAFIAS); 46 PE teachers, swimming trainers and instructors (19 males and 27 females) consented to participate. They all taught elementary school pupils. Results: During swimming classes, pupils spent most time on motor activities (77%) or waiting for teacher's instructions (13%). Specific competences and higher education were found to play a significant role in achieving good results in teaching swimming. Conclusions: Teacher's qualifications and education level, together with a detailed demonstration, play the main role in selecting instruction modes and the motor engagement of pupils. (Contains 5 tables.)