As a junior, he was the starting point guard on Poly's basketball team that went 30–1 and won the Southern Section 4A title. The final was played before over 10,000 fans at the Long Beach Arena, where Gwynn scored 10 points in the 69–50 victory over Buena of Ventura. His teammates included Michael Wiley, who became a professional player in the National Basketball Association (NBA). In his senior year, Poly was 23–7, and again advanced to the championship round in spite of finishing third in the Moore League. Their bid for a second straight title ended with a 57–50 loss to Pasadena. Gwynn averaged 10.3 points and totaled 178 assists for the season, and he was named to the All-CIF Southern Section Second Team. After the season, he switched to baseball, whose season was already well underway. Despite his shortened season, he earned first-team All-Southern Section honors after batting .563. Poly's baseball teams struggles taught him to remain focused and continue to execute and stay productive.