Sesame Street Walking Letters was one of the earliest lines of Sesame Street toys, produced by Educational Toys, Inc. (a division of Topper Corp.) in 1971. The sets featured plastic letters that "walked" on little feet down a ramp or across a table.
Big Bird's Basic Walking Letters Set included a ramp and a set of six walking letters. In 1972 it was produced in Canada by Irwin Toy under license from Educational Toys, Inc.
Big Bird's Blunderproof Walking Letters Set was more elaborate, with twelve correcting keys, 7 letters (C, H, O, M, P, T, A) and a ramp with a box at the end that judged whether a combination of three letters spelled a word correctly. The child playing with the toy selects a picture of a three-letter word, like a cat, or the sun. The child inserts the picture piece into the slot, and then spells the word out with walking letters. If the word is spelled correctly, a figure of Big Bird pops out of the box to reward the child. If the word is spelled incorrectly, the offending letters fall off of the ramp.
The letters were also sold separately.