Complex sentence: This allowed the school to increase the intake from one class to two classes (from about 30 students to about 60) resulting in the number of the pupils increasing to around 350 over a period of about five years.
Split into simpler sentences: This allowed the school to double its intake from one class to two classes (30 students, up to 60 students). The number of the pupils increased to around 350 over a period of five years.