The current study has aimed to compare the objectives, content, teaching-learning process, and evaluation dimensions of the International Baccalaureate Diploma Program (IBDP) Language A1 Course teaching program with those of the teaching programs of high school 12th grade Language and Expression and Turkish Literature courses in relation to critical thinking skills based on the opinions of students within a Turkish context. The present study adopted a qualitative research method and employed a case-study design. The study was conducted in Istanbul Prof. Dr. Mümtaz Turhan Social Sciences High School, which was the first and only state school implementing IBDP in Turkey during the fall term of the 2011-2012 school year. The study group was composed of 11 twelfth graders from this high school who participated in the IBDP and 15 twelfth graders participating in the national program. The study's data were collected through semi-structured interviews conducted with the students. The collected data were structured in the Nvivo 9 qualitative data analysis program and then analyzed by means of content analysis. At the end of the study, based on the students' opinions, it was concluded that although the objectives, content, learning-teaching process, and evaluation of the Language A1 Course made greater contributions to the development of students' critical thinking skills as compared to those of the Turkish Literature and Language and Expression Courses, there are several problems in implementing the IBDP in Turkey.