Complex sentence: From the first to the fourth grade, children stay in one classroom and have one class or form and one teacher which teaches all subjects, except on some occasions, sports, art and music are taught by separate teachers or is supervised by the appropriate teacher.
Split into simpler sentences: From the first to the fourth grade children stay in one classroom, have one class or form and one teacher. In some schools, sports, art and music are taught by separate teachers or are supervised by an appropriate teacher.