Slovak language and literature belongs to the leading subjects in the system of secondary education in the Slovak Republic. The persistent traditional teaching techniques (encyclopedic-memorization) and the absence of systematic development of critical thinking in the process of education has caused an identified below average state of critical thinking of students at secondary grammar schools. The aim of our half-year experiment was to verify the effectiveness of The Programme of Development of Critical Thinking of Pupils in the Subject of Slovak Language and Literature. To meet the set target we implemented an experiment (a single-factor technique of parallel groups). Out of 16 first-grade secondary grammar schools classes (