Background: The aim of the research was to determine an influence of an increased number of outdoor lessons of Physical Education on aerobic fitness and to evaluate students’ attitude towards endurance efforts. Material/Methods: In the presented research project a group of students participated in a school program of Physical Education on the basis of a higher number of lessons realized in the natural environment in the vicinity of school. The subjects were a group of 220 students from 4 schools of the Pomeranian Voivodeship, who were subjected to initial and final measurements during two school years. The most important assumption of the research stated better effects of outdoor classes of Physical Education in comparison with indoor classes and the shortage of experimental factor influence on the correlation change between objective and subjective indices of fitness and attitudes related to it. Results: In the experimental group the most distinct differences between initial and final tests concerned the endurance measurement, similarly to the control group in which, however, the improvement in the final test was less noticeable. The correlation among three analyzed variables was significant for both research groups. The comparison of results of students from the experimental and the control groups demonstrates a positive influence of outdoor lessons on the level of endurance and, to a lower degree, on the feeling of effort fatigue and mood. Conclusions: The research was conducted with a use of three research tools: the mood scale, Cooper’s test and the subjective fatigue feeling with finished effort scale that allow a positive verification of the presented hypothesis, which should be an encouragement for wider practicing of innovative activities to bring closer the assumed aims of Physical Education to the aims actually achieved.