In 1896, four Baltimore families hired a German schoolteacher, Fraulein Martha Auguste Schurmann, to conduct traditional kindergarten classes for their children. Pleased with the children's progress, they quickly decided to build on their success. They researched the best primary school methods, and in 1897, opened a school for 15 students in kindergarten, first, and second grades. It was called the Boys' and Girls' Primary School and located above a pharmacy in Baltimore City.

Within two years, the school grew to 79 students and 12 teachers and changed its name to Calvert Primary School. Virgil M. Hillyer, a Harvard graduate, was named the first Head Master. Hillyer would go on to gain a national and international reputation as an innovator in primary and elementary education, an author of children's books, and the founder of Calvert's Home Instruction Department in 1906.

In 1901, the school moved into a new building on West Chase Street, and twenty-three years later, the school moved to its current location in Roland Park. The most significant expansion occurred in 2000 when the Board of Trustees approved a plan to create a Middle School. Property was purchased across Tuscany Road, and a new state-of-the-art school was built to house Fifth through Eighth Grades.

Today, Calvert School serves over 600 boys and girls beginning in Fifth Age through Eighth Grade.