I would hardly call Jon Stewart a liberal, much less a leftist, and I don't remember him ever calling himself either of those terms either. He's a centrist with some fairly rightwing positions (like continued support for the occupation of Afghanistan), but since he's not thumping a Bible or calling for an end to all taxes on wealthy people he appears pretty much communist in our political landscape.
But, like me, his mother was a teacher, and I'm glad that the recent attacks on teachers are making someone in the media as peeved as they're making me. It's a thankless job that requires a college degree, takes more than 40 hours a week, and takes years of experience to get good at. At the same time, they're one of the last strong unions still standing in the US and teachers are almost entirely separated from profit and careerist motives, making them the enemies of the corporate state.
Here's a clip from a week ago in which Stewart points out how ridiculous some of these attacks on teachers are.