Walberg became head coach of Mountain View (Calif.) High at age 22. He also served as badminton coach at James Logan High School (1983–84) and head basketball coach at Los Altos High School (1981–83). Walberg then became the head coach at Newark (Calif.) Memorial High School for five seasons (1985–89), winning one league title on two trips to the championships. In 1990, he embarked on a 13-year tenure as head coach at Clovis West High School in Fresno, Calif. In 1997, he had his Clovis West High team adopt his AASAA offense, leading to a 159-18 five-year record.