A sketch where Roosevelt Franklin tells the story of "Morty Moot Mope" is on YouTube:
I saw images from this sketch on Muppet Wiki today, and assumed that the person who got the images got them from a foreign dub, but then I found the clip and it's in english!
And a portion of this story was featured in "Sesame Street Unpaved", only titled "Same Sound Brown" and showing images from a different sketch.
It sounds like Roosevelt refers to one classmate as "Suzetta Something". I'm not too sure if I'm right about the last name.
Interestingly, Same Sound Brown sounds more like David than he does in the "Sound it Out" clip.