Developing the awareness of one's level of physical activity is an important prerequisite to change one's lifestyle into a more physically active and healthy style of living. The aim of the study is to verify the efficacy of pedometers in educational environments and to specify the differences between physical activity in boys and girls aged 17. Twenty seven boys and thirty seven girls from randomly selected classes in two high schools in Katowice, Poland participated in the study. Students wore Yamax SW-700 pedometers for three weeks, continuously recorded data from the pedometers, and used the motivational feedback booklets. The three-week intervention using pedometers was complemented with the IPAQ questionnaire to assess their physical activity during the last seven days.For statistical analysis, we used basic statistical characteristics, Mann-Whitney test, repeated ANOVA, "effect size" coefficient ω2 (Tolson, 1980), and other partial analysis programs in Statistica 6 and SPSS 15.Both boys and girls were less physically active on weekend days during the analyzed period. The use of pedometers did not decrease the difference between physical activity on school days and weekend days. No significant differences were found in the average number of steps per day between boys and girls, as well as no significant differences were identified in the interaction of gender vs. school and weekend days.Additional study is necessary to confirm whether the use of pedometers in physical education classes can help decrease the differences in physical activity between boys and girls.