The document summarizes the Spanish education system. It is divided into four levels: optional pre-school from ages 3 to 6, compulsory primary school from ages 6 to 12, compulsory secondary education from ages 12 to 16, and post-16 Bachillerato which includes sciences, social sciences, humanities and arts. Students must pass the PAU exam to enter university, where most degrees are 4 years. Schools are state schools, privately run schools funded by the state, or purely private schools. Class sizes are typically 25 students per teacher but decrease if a student has special needs.