While at Pinole Valley High School, Dirnt and classmate Armstrong formed a band called Sweet Children. Dirnt's mother struggled to provide for him and his sister as a single parent, and eventually had to leave Rodeo in 1987 to look for work. Unwilling to leave Sweet Children, Armstrong and Dirnt convinced each other's parents to allow Dirnt to move into Armstrong's garage. After drummer John Kiffmeyer, who was also known as Al Sobrante, joined the group and replaced original drummer Raj Punjabi, Sweet Children began performing at 924 Gilman Street. The band performed several well-received sets, which encouraged Armstrong to drop out of high school to focus his energy on music. Dirnt, however, worried that he needed a backup plan and continued his studies. Bass player Sean Hughes, who was not as dedicated to the group as the other members, left Sweet Children, leaving Dirnt to play bass. Dirnt often brought his bass to school, and the plucking noise of the unamplified strings led classmates to jokingly call him by the onomatopoeia "Dirnt". After changing its name to Green Day, the band recorded its debut album "39/Smooth" over the 1989 Christmas holiday break and went on its first van tour in June 1990, leaving the day that Dirnt graduated from high school.