Health topics in the Curriculum of the subject Nature and Society are one of the basic determinants for the physical, mental and social development of students. The inclusion of Health Education in the Croatian education system in 2012 encouraged the integration and correlation of health topics with other subjects. The aim of the research was to determine whether the education of students on the topic of the respiratory system, infectious diseases and COVID-19 affects their knowledge about it. The study included 33 fourth-graders. The experimental group consisted of 15 students and the control group of 18 students. For the purposes of the research, a 10-question exam was prepared, which was distributed to the experimental group before and after active research classes, and to the control group, given that it had education in traditional classes only once. The results of the study show the existence of a statistically significant difference before and after education on the respiratory system, proper hand washing, infectious diseases and COVID-19 in the experimental group. After the education, the experimental group washed their hands for a long time, which was one of the goals of the education, and they started to wash the upper part of the hand, the thumb in particular and turn off the pipe tap more carefully. Differences are also evident in the understanding of the impact of physical activity on respiration between the experimental and control group, in which the control group handle the issue more successfully. There was no statistically significant difference in lung-to-organ and organ-to-lung gas transmission, although the results in both groups were on the verge of significance about education. The virus as a pathogen of COVID-19 disease was recognized by both the experimental and control group not showing the difference in knowledge, regardless of education.