Not many school districts offer summer school. But you can send your child to an academic camp and they will be actively engaged in learning, and have fun in a creative way at the same time.
The choices for academic camps range based on the subject you want your child to focus on. Some camps, like Stratford Summer School Programs, which are located throughout the Bay Area, are oriented toward elementary and middle school children and are a general enrichment program that focuses on many subjects. iD Tech offers computer and technical programs as a day or overnight experience at major universities.
Besides the typical math, reading, and writing camps, there are camps that focus on other important academic facets also. Chess camps and language camps are good academic alternatives as well as community service camps or leadership camps.
Another alternative is tutoring for those subjects where help is needed. Many tutors will hold sessions in your home and offer flexible times so that you can in other fun activities through the summer.