Complex sentence: Almost all pupils at Horris Hill are boarders although there are a few day boys, however it is a requirement that all boys board at the very latest from the beginning of the September term following their eleventh birthday.
Split into simpler sentences: Almost all pupils at Horris Hill are boarders although there are a few day boys. It is a requirement that all boys board at the very latest from the beginning of the September term following their eleventh birthday.