This may depend on your family circumstances; you should take in to consideration the year group of entry, for an expatriate family that may have frequent moves it is important to ensure stability of education, particularly for the two year GCSE and Sixth Form programmes. Entry to Year 9 (age 14) is popular as it gives the child one academic year to settle in to boarding life, make friends and get to know the teachers before selecting their GCSE options for Years 10 and 11.
Entry to Year 12 (the Sixth Form) is a good stepping stone to university as it encourages independence in a safe secure environment and provides the opportunity for students to visit university open days.