When the Lagunitas School District was seeking a new superintendent this year, Ashley Fullerton participated in a hiring workshop with a middle school social studies teacher named Yosha Bourgea. She hadn’t spent much time with him before, but the first-year teacher expressed a happy enthusiasm for the district, according to Ms. Fullerton. He seemed dedicated to his students, whom he said genuinely loved to learn—a trait not to be taken for granted among pre-teens. Ms.…