A few weeks before summer break, an eighth-grader in Fairfax County was pulled from his civics class and led into an office. An assistant principal told him that classmates had reported hearing him say he’d smoked marijuana with five other boys — days earlier, after school hours, off campus. A uniformed police officer joined the interview. The boy did not want to talk, his mother, Dawn Daugherty, later said, but did so after the officer told him to confess or risk “doing time.” Fairfax school officials said there was no such threat. They said the boy was told what other students had said and about the importance of telling the truth.