While traditionally a key piece of English schools (especially English boarding schools), the house system has also come to be a common aspect of school culture in many classical Christian schools.
House systems vertically integrate students. Without such integration, each class often develops its own identity and culture. While this is natural and good in many respects, classes can develop cultures different, distinct, and separate from other classes. These identities are driven not just by the personalities of those in the class but by the natural inclinations and aptitudes, both academic and moral, pertaining to ages and stages in development.
Thus, while students bond together, they maintain a separation by age level. The first, a sense of natural leadership, service, encouragement, yes, even admonishment, from elder to younger. The second, a sense of natural reception of encouragement and service and a striving for emulation of those qualities of Christ-like leadership from younger to elder.