A former Los Angeles elementary-school teacher was arrested Wednesday for molesting 20 children, police said. Prosecutors filed 15 charges, including sexual abuse and lewd acts on a child, against Robert Pimental, 57, who was a teacher at George de la Torre Jr. Elementary School in Wilmington. The charges stem from an investigation that begin in March and involve a dozen children, although detectives say Pimental preyed on an additional eight girls. This is only the latest allegation to hit L.A. schools—an audit released in November found that the nation’s second-largest school district had failed to promptly report 150 cases of teacher misconduct.