The main objective of the study was to determine the impact of immediate verbal feedback on swimming effectiveness. Swimming effectiveness was expressed in the subjects reaching their objective, i.e., maximum swimming velocity. The study involved 64 subjects divided into two groups (experimental group n=32; control group n=32). Two measurements - initial (pre-test) and final (post-test) - were conducted. The subjects swam a distance of 25 m front crawl at maximum velocity. The experimental groups received immediate verbal feedback focused on stroke lengthening, as a shorter stroke length is regarded as the most common reason behind lower swimming velocity. From this perspective, lengthening the stroke is important due to its relation with mechanics and energetics in all styles of swimming. The control group received no verbal feedback. All tests were recorded via video cameras (50 samples·s-1). The analysis of the kinematic movement parameters (horizontal average swimming velocity over 15m, time achieved over 15m) was carried out by means of the SIMI Reality Motion Systems 2D software. Analysis of variance with repeated measurements with a Tukey’s test demonstrated statistically significant differences (p<0.05) in the tested groups in the case of the kinematic parameters measured in the study. Immediate verbal feedback (IVF) caused an increase of the average horizontal swimming velocity by 2.92% (0.04 m·s-1). Consequently, the average time needed by the swimmers to cover the distance (15m) decreased by 2.94% (0.36s). The results confirmed the effectiveness of the proposed method of teaching and improving the swimming technique using IVF.