Complex sentence: Twynham School (also known as Twynham Comprehensive School) is a comprehensive school in Christchurch, Dorset which has approximately 1,500 students covering years 7--13 (ages 11--18).
Split into simpler sentences: Twynham School (also known as Twynham Comprehensive School) is a comprehensive school in Christchurch, Dorset. There are approximately 1,500 students in the school covering years 7--13 (ages 11--18).