The education system in Singapore is highly uniform. The curriculum is followed by teachers, who prepare their students for exams. In addition to textbooks, worksheets, drills, and practice, they are heavily dependent on textbooks. Singapore has a six-year primary school system, followed by four to six years of secondary school, and one to three years of postsecondary school. In primary schools, the curriculum is the same for all students from years one through four. The first year of primary school is free. After the fourth year, students are streamed according to ability. A Primary School Leaving Examination is administered at the end of primary school, and the results determine the secondary school students will attend. Secondary education varies according to the school and program type. All students enrolled in the express and normal (academic program) are required to study English, their mother tongue language, math, science, as well as geography, history, and English literature. At the secondary level, students take subject-based exams based on their band.