Great teachers tend to be good-natured and approachable, as opposed to sour or foreboding; professional without being aloof; funny (even if they’re not stand-up comedians), perhaps because they don’t take themselves or their subject matter too seriously; demanding without being unkind; comfortable in their own skin (without being in love with the sound of their own voices); natural (they make teaching look easy even though we all know it isn’t); and tremendously creative, and always willing to entertain new ideas or try new things, sometimes even on the fly.

Passion. Of all the qualities that characterize great teachers, this is the most important, by far.

Don’t think, by the way, that students don’t pick up on the disdain. They absolutely do. And my experience with evaluating faculty members over the years suggests that the teachers who are most widely disliked are the ones who most dislike students.

State test results showed that students in private voucher schools performed significantly worse in math and about the same in reading as their public school counterparts.

or has Milwaukee’s voucher program met the promise of increased parental satisfaction. A longitudinal study on achievement, in its final report, noted that only17.5 percent of the voucher students remained in a voucher school after five years. The comparable figure for the public schools was 43.5 percent.

Vouchers are a vehicle to funnel tax dollars into private schools. Using the false promise of “choice,” they are an unabashed abandonment of public education and of our hopes for a vibrant democracy.

On Wednesday, Mr. Gardner will celebrate his 95th birthday with the publication of another book — his second book of essays and mathematical puzzles to be published just this year. With more than 70 books to his name, he is the world’s best-known recreational mathematician, and has probably introduced more people to the joys of math than anyone in history.