I checked current reports, and I could not verify a shooting at a South High School in California. There are several schools with that name, while a recent South High lockdown incident I found was at Lakeville South High School in Minnesota, where authorities said no injuries or acts of violence had been reported.

For a responsible news post, I’d use wording that does not present an unverified shooting as fact:
A reported security incident involving South High School has prompted an emergency response, with authorities working to assess the situation and ensure the safety of students, staff, and others in the surrounding community.
Officials have urged people to remain calm, avoid the area if directed by authorities, and rely on verified information from law enforcement and school officials rather than unconfirmed reports circulating online.
At this time, details surrounding the reported incident remain limited, and information may change as authorities continue their investigation.
This is a developing story. Additional details regarding the nature of the incident, whether any injuries occurred, and the status of the school are expected as officials release more information.
Please avoid sharing unverified claims about an active shooter or shooting until those details are confirmed by authorities.
If you have the specific California city or the name of the South High School, I can turn this into a verified reporter-style article with the correct details.