Complex sentence: In common with many boys' boarding schools, every student must participate in a "fitness-oriented athletic offering" at least two seasons of the year; at the same time some boys attend the school preparing for a life as a professional athlete.
Split into simpler sentences: In common with many boys' boarding schools, every student must participate in a "fitness-oriented athletic offering" at least two seasons of the year. At the same time, a number of boys attend the school each year preparing for a life as a professional athlete.