Wikipedia reports on his early life:
Bernie Sanders was born on September 8, 1941, in Brooklyn, New York, the son of Eli and Dorothy (Glassberg) Sanders. His father was a Jewish immigrant from Poland whose family was killed in the Holocaust. His mother was born to Jewish parents in New York.
Sanders attended elementary school at P.S. 197, where he won a state championship on the basketball team. He attended Hebrew school in the afternoons and had his bar mitzvah in 1954. Sanders attended James Madison High School, where he was captain of the track team. While at Madison, Sanders lost his first election, finishing last out of three for the student body presidency. Sanders's mother died in June 1959 at the age of 46 shortly after Sanders graduated from high school. Sanders went to Brooklyn College for a year before transferring to the University of Chicago. While there, he was active in the Civil Rights Movement, and a student organizer for the Congress of Racial Equality and the Student Nonviolent Coordinating Committee. One of the actions he took was the coordination of sit-in protests against segregated campus housing. Sanders also participated in the 1963 March on Washington for Jobs and Freedom. He was a member of the Young People's Socialist League, the youth affiliate of the Socialist Party of America.
He graduated from the University of Chicago with a bachelor of arts degree in political science in 1964. After graduating, Sanders spent several months on an Israeli kibbutz, and he moved to Vermont in 1968.