The driver, 16, hit the 25-year-old rider while making a left turn off Danville Boulevard into the parking lot of San Ramon Valley High School at 3:30 p.m., police said.
The bicyclist, who was riding with two other people, was taken to Kaiser Permanente Medical Center in Walnut Creek with a broken collar bone. The other cyclists were not hurt. No arrests were made.
Police, town staff and the school district's Street Smarts program have been making an extra effort lately to educate kids and teens about bike safety. Still, Friday's accident is the fourth of its kind in the San Ramon Valley in a month.