Complex sentence: In 1931 the School moved into the Russell Sage Building at 122 East 22nd Street, then, in 1949, the School moved to the Andrew Carnegie Mansion at 2 East 91st Street.
Split into simpler sentences: In 1931 the School moved into the Russell Sage Building at 122 East 22nd Street. In 1949 the School moved to the Andrew Carnegie Mansion at 2 East 91st Street.