Complex sentence: S3 is still considered to be with the Broad General Education (or BGE) phase; however some schools allow students to start to narrow which subjects they wish to study, with certain compulsory subjects such as English and Mathematics.
Split into simpler sentences: S3 is still considered to be with the Broad General Education (or BGE) phase. Some schools allow students to start to narrow their field of study, with exceptions for compulsory subjects such as English and Mathematics.