If you are an incoming freshman into high school-there are few academic summer school options for you. Some local community colleges offer summer programs and there may be space available for a summer program or if programs are still recruiting students like the Design Immersion Days Program offered through the Southern California Institute for Architecture.
Another recommendation for incoming ninth grade students is to start volunteering! Offer your services at a local community garden, at the zoo, in the local library, at the YMCA or Boys and Girls Club. If you are involved with organized religion, there may be summer opportunities available for you to help out.
Students currently in grade 9 and 10 should also volunteer, find summer work, search for additional programs that are of interest to the student. If you are college bound, remember that colleges prefer students not that are necessarily "well rounded" but that have found a particular niche in their community (in addition to maintaining a strong academic profile). Colleges are searching for students with character.
Students that may have gotten less than a C (meaning a D or Fail) in an academic class that could satisfy an A-G requirement should retake the course during summer school or at a local high school that offers credit recovery or remediation. Due to severe restraints with LAUSD, summer school is offered only for current 10th and 11th grade students that have earned a D or Fail in an academic class.
For those students that want to finish high school early, have a desire to attend UCLA, and want the most financially savvy means for pursuing a post secondary education, I recommend an early college program similar to the Ralphe Bunche Scholars Program offered through LA City College.
Students can also register NOW to take courses in the fall while they are concurrently enrolled in traditional high school. See more details here!
The worst thing a high school student can do during the summer is sit around and watch TV or play video games the entire time. While that may be permissible for an hour or so, the idle time for your brain can be an incredible detriment to you in the future.