The Helen Bush-Parkside School grew to incorporate a boarding house. In the 1930s, Upper School boarders lived in the lovely Ostrander home on Lake Washington, which had been loaned to the school by a parent. The boarding house was called Rosemary Hall, after Rosemary Ostrander Ballinger, a member of the 1935 graduating class and one of the first lifers, beginning her education with the 1924 kindergarten class.