The assessment of students' academic achievement via international monitoring studies provides important insights to participating countries. Besides the cognitive performance of students, educational equity is one of the emphasized topics within the scope of Programme for International Student Assessment (PISA) study. Results regarding educational equity are quite important in Turkey because academic achievement differences among school types are relatively high in Turkey. Although a wide range of studies is conducted to examine the performance differences between school types in Turkey, it is observed that most studies focus on mean scores of school types. The aim of this study is to examine the change in student ratios at a basic- and advanced level of proficiency by school types in PISA applications between 2003 and 2018. Results show that approximately all students in science high schools and social sciences high schools have basic proficiency in all literacy fields and throughout PISA 2003 and PISA 2018. The ratio of students with basic proficiency in Anatolian high schools and Anatolian imam hatip high schools tends to be increased. However, the ratio of students with advance proficiency seems to be low in all school types in Turkey except science high schools. Steps to decrease the achievement differences between school types in Turkey within the scope of findings are suggested.