Introduction. Critical thinking is increasingly in demand in professional activities and private life, however, education systems do not fully answer to the request of its formation yet. The main solution is usually considered to be the implementation of exercises on critical thinking in subject classes. Practice shows that effective implementation of such exercises requires the formation of an educational environment in which initiative and independent activity of a student are encouraged. Theoretical analysis. The importance of the environmental factor might be explained by Self-determination theory: satisfying a child’s need for autonomy contributes to academic motivation, which mediates the influence of the environment on achieving meta-subject educational results. Empirical analysis. The connection between modality of school environment and levels of critical thinking of 7th grade students is considered. The correlation of the number of students at the «advanced» and “developing” levels with a type of environment identified on the basis of two scales, freedom and activity, is shown. Conclusion. The results of the study confirm the importance of environmental stimulation of activity for the formation of critical thinking in secondary school, especially in combination with freedom, i.e. personalization, priority of personal interests, possibilities for independence of judgments, choices and actions.