Encinal Junior & Senior High School
I would recommend checking out Encinal High School in Alameda. It's a smaller public high school (~1,100 students), with the full range of sports and music, and with a diverse student body, and a supportive environment. I'm not sure exactly what the class sizes are, but I think they are consistent across all Alameda high schools, and I know there has been a lot of attention to creating smaller class sizes when possible. Nice community on the west end of Alameda (where Encinal High pulls from), and quick commute to Oakland.