Complex sentence: He attends Junipero Serra High School in Gardena, California, and helped the school's baseball team win the California Interscholastic Federation Southern Section division championship in 2013.
Split into simpler sentences: He attends Junipero Serra High School in Gardena, California. He then enrolled at Junipero Serra High School in Gardena, California, where he helped the school's baseball team win the California Interscholastic Federation Southern Section division championship in 2013.