Nanette Asimov:

Oakland police have opened an investigation into the case of a first-grade boy whose skull was fractured Monday when, he said, an older student slammed him against a tree as he waited for a ride from his daycare provider.
Police investigators will visit Piedmont Avenue Elementary School today to question school officials and any students who might have seen what happened.
Seven-year-old Zachary Cataldo spent two nights in the intensive care unit at Children’s Hospital before returning home on Wednesday.
“After our investigation, the district attorney could very well decide to prosecute and file charges,” said Officer Roland Holmgren, spokesman for the Oakland police.
Vince Matthews, state administrator for the Oakland Unified School District, and other district officials did not return calls from The Chronicle on Thursday. Nor did Principal Angela Haick of Piedmont Avenue Elementary, where the incident took place.
But expressions of concern for Zachary – and outrage at what his father said was the school’s lax response to repeated bullying incidents – poured in from across the country after the story appeared in The Chronicle on Thursday.

Much more here and here.