Investors led by Camden Partners have closed a deal to buy Calvert Education Services for an undisclosed amount, according to a source.

Calvert runs a lower and middle co-educational private school with a day school operation in Baltimore. A leader in distance learning for over a century, Calvert serves schools and students in all 50 states and over 60 countries. It also runs a virtual school.

Calvert is led by CEO Richard Rasmus, who previously led K12 Inc. He has an MBA degree from Harvard Business School.

Baltimore-based Camden Partners is a private equity firm providing growth capital to lower-middle market companies, primarily in education, healthcare, and business services. Since its founding in 1995, the firm has raised four funds, and invested in over 60 companies, generating 9 IPOs and 16 sales to strategic and financial buyers.