Mild-mannered, soft-spoken, and beaming broadly, the Microsoft chairman Bill Gates looked every bit the benevolent businessman as he took the stage at the Toronto International Film Festival on Saturday evening, to help plug the education-reform documentary “Waiting for ‘Superman.'” Mr. Gates appears in the film, and, with his wife Melinda, heads a foundation that has invested heavily in improvements to education. But his aw-shucks manner couldn’t hide the fact that some of the proposals he tossed off on stage at the Winter Garden theater here were volatile stuff. “We’re investing in building these evaluation systems,” Mr. Gates said. He was referring to systems that would evaluate the performance of public school teachers, with an eye toward ending the current tenure system under which many teachers now work, and providing a way to weed out the worst teachers, while, perhaps, rewarding the best. He also mentioned, at least twice, changes to teacher pension systems.