Kaplan did not grow up religious and was known as "Len". His family only had a small connection to Jewish practice, but he was encouraged to say Kaddish for his mother. On his first day at the minyan, Henoch Rosenberg, a 14-year Klausenburger Chassid, realized that Len was out of place, as he was not wearing tefillin or opening a siddur, and befriended him. Henoch Rosenberg and his siblings taught Kaplan Hebrew, and within a few days, Kaplan was learning Chumash.