 One of their great-grandfathers was Samuel McClellan of Woodstock, Connecticut, a brigadier general who served during the Revolutionary War.McClellan initially intended to follow his father into the medical profession, and attended a private academy, which was followed by enrollment in a private preparatory school for the University of Pennsylvania.He began attending the university in 1840, when he was 12 years old, resigning himself to the study of law after his family decided that medical educations for both McClellan and his older brother John were too expensive.