Sal Khan, the chief executive of a nonprofit education group, gave a TED Talk last spring predicting that A.I. chatbots would revolutionize education. He believes that giving every student an artificially intelligent personal tutor could transform the field. Khan’s vision taps into the Silicon Valley dream of automated teaching platforms that customize lessons for each student. Proponents argue that these systems could close achievement gaps by delivering individualized instruction faster and more efficiently than human teachers.