WASHINGTON—More workers were involved in strikes and other labor disputes in 2018 than at any point in the past three decades, fueled by widespread teacher protests last spring, according to data released Friday by the Labor Department.

Almost 500,000 workers participated in work stoppages last year, driven primarily by protests in the education, health-care and social-assistance industries, the Labor Department said. Overall, there were more such disputes than in any year since 2007, and more people on strike or lockout than...