D'Snowth: Originally, the show's writers taught numbers only as high as ten; they didn't raise the limit to 20 until a few seasons later. Even then, only numbers in the 2-12 range could be numbers of the day. (Higher and lower numbers gained that status in the early 80s; the "long count" limit rose from 20 to 40 during those same years.) It's a shame that Sesame Street has been stripped down for a pre-K audience, since some of the 1980s number sketches were very well done: a typical child in first or second grade would easily understand the "40 Blocks to School" song, emotionally as well as mathematically.