We all have ideas why certain characters left. But does anyone know for sure why? Also, what happened to the characters that left? I don't think they explained any of them.

Anthony Tyler Quinn - During season five of "Boy Meets World", Quinn was on the FOX sitcom "Ask Harriet". I'm assuming he left his role as Mr. Turner, who during season 4 seemed to be just a recurring character, in order to star in his own show. Unfortunatly (for him), "Ask Harriet" only lasted a few episodes. As for the character of Mr. Turner, the gang went to a new section of the school, the senior hall. Maybe, at that point, Mr. Turner didn't teach seniors, and therefore didn't see them. In seasons 6 & 7, Cory, Shawn and Topanga were in college, so then of course they wouldn't see him.

Some say they thought he died at the end of season 4, but that joke in the graduation episode proves that he's alive and still at the school. Plus I think if he died, they would have made a bigger deal about it.

Lily Nicksay - Beginning with season 3, Morgan was played by Lindsey Ridgeway. WHY?

Lee Norris - Maybe they felt he wouldn't fit in with the show anymore. As for the character, he just hung out at "the other side" of the school, only to show up again in the graduation episode. After that, it's pretty obvious he went to a different college from the gang.

What about the others, including Mr. Williams, Harley Keiner, Joey the Rat & Frankie?

For Morgan we are pretty sure she left the show because they wanted an older actor. Your explaination of Mr. Turner seems really acurate.

I've always heard that Quinn left the show to work on Broadway. He obviously taught seniors because he was Eric's teacher in the third season. As for why he joined another sitcom, I don't know. Ruins my explanation.

With Turner gone, there was really no need for Williams, I suppose.

Joey the Rat and Frankie popped up again during the graduation episode. It's actually strange because Joey had left the school and Frankie was alone and had turned into a good guy. In graduation, Joey was back and they reverted Frankie back to a thug with him. Of course, they were a bit softer without Harley, so it was okay, I guess.