When Blue's CLues was on public TV I had a 5 year old son did not speak. He was glued to that show whenever it came on. Due to an autistic wiring problem in his speech centers it engaged him in a conversation that allowed him to participate without any self consciousness. Of course his other favorite shows were Jeopardy Wheel of Fortune and most of all WHo Wants to be a Millionaire.
WHen he needed to speak to us in sentences he would use the computer and type out his thouts in Microsoft Word.

SUre Sesame St was a big help but Blue's Clues had a special format that allowed him to converse mentally to the point that at the age of 6 he started vocalizing. At first is was word responses but the progress then became more rapid than a child of 3 or 4.

It was a big deal when the main character on Blue's Clues went to college.