From wikipedia, I remember reading about this in "Tipping Point";
Blue's Clues was created by a creative team led by Todd Kessler -- who was at the time a writer-director -- and producer at Nickelodeon and researcher Angela Santomero. Kessler and Santomero hired cut-out animator Traci Paige Johnson to collaborate on the pilot. (Johnson would eventually provide Blue's voice. A child voice actor filled in for part of season 2.)
Kessler had previously worked on the PBS children's show Sesame Street, and both he and Santomero hoped to build on and improve that model of educational programming. "We wanted to learn from Sesame Street and take it one step further," said Santomero.[1]
"I love Sesame Street," said Kessler. "But I always believed that kids didn't have short attention spans, that they could easily sit still for a half an hour."[2] While Sesame Street was originally organized around short, commercial-like segments, each Blue's Clues show is a single extended narrative.
"There was...a theoretical perspective at the time, based in part on Piaget, that a preschool child couldn't follow an extended narrative," according to Daniel Anderson, who helped develop Blue's Clues for Nickelodeon. In the early 1980s, however, research suggestive that narrative was in fact a crucial way that small children organized their experiences.[3]
The show also uses phrase repetition and a minimum of editing in an attempt to avoid confusing its young audience.[1]
Blue's Clues was extensively analyzed by Malcolm Gladwell in his bestselling book The Tipping Point. According to Gladwell, the show was carefully designed, using methods pioneered by Sesame Street, to encourage its educational messages to "stick" in a child's mind.