This master's thesis aims to explore the potential of a selected textbook to develop critical thinking in learners of a secondary school at English classes. The thesis is divided into theoretical and practical parts. First, the theoretical basis of the constructivism instruction in education is set. The discussion of the connections between critical thinking and constructivism follows. The analysis of the textbook Global Pre-Intermediate constitutes the core of the practical part of the thesis. Based on the results of the analysis, certain modifications of the activities designed as to provide learners with more opportunities to develop critical thinking, are suggested.