Complex sentence: She attended St Hilda's School, Westcliff from the age of 3 to 11, then moved schools, attending Westcliff High School for Girls from the age of 12.
Split into simpler sentences: She attended St Hilda's School, Westcliff from the age of 3 to 11. She then moved schools, attending Westcliff High School for Girls from the age of 12.