It was a big day for the kids in Mr. Ratburn’s grade-school class — and, by extension, the children (and parents) who watch the long-running PBS Kids series Arthur. In today’s Season 22 premiere of the animated show, Arthur and his friends learn that their teacher Mr. Ratburn was going to be married. What none of them was expecting is that he is tying the knot with an aardvark named Patrick. The episode, titled “Mr. Ratburn and the Special Someone,” shows the teacher taking a cell phone call while preparing to hand out a pop quiz on homework.