While she was president of Wellesley College from 1949 until her retirement in 1966, the college's resources and facilities were expanded substantially. Clapp was a strong advocate of careers for women. She was elected a Fellow of the American Academy of Arts and Sciences in 1952.
After leaving Wellesley, Clapp served briefly as administrator of Lady Doak College, a women's college in Madurai, India, then as United States cultural attaché to India, then as minister-councilor of public affairs in the United States Information Agency until her retirement in 1971. The library at Wellesley is named for her.