http://www.bonethefish.com/viewtopics.php?1535

Welcome Back, Kotter is an American television sitcom that originally aired on the ABC network from September 9, 1975 to June 8, 1979. The show starred comedian Gabe Kaplan as the title character Gabe Kotter, a wise-cracking teacher who returns to his high school alma mater - the fictional James Buchanan High in Brooklyn, New York - to teach an often unruly group of remedial wiseguys known as the "Sweathogs." The school's principal was an absentee; the uptight vice principal dismissed them as worthless hoodlums and only expected Kotter to attempt to control them until they inevitably dropped out.

It's the most obvious conclusion, but the fourth season, which saw the show make some very dubious changes and wasn't the same show that had aired the first three seasons.

sometime during the beginning of season 3

When Vinnie and Kotter left, it became a shadow of it's old self.

When Vinnie and Kotter left, it became a shadow of it's old self.

Yep, this is the easiest "bone the fish" call ever made. Wasn't even worth having on the air after that point.

What ruined this show was the backstage bickering between Gabe Kaplan and the producers which ended up with Gabe's departure from the cast.

I voted for It's a girl(s). By season 3 the show just wasn't the same and it was getting stale. Suddenly Mr. Kotter wasn't a sweathogg anymore and he almost became a standup comedian during that season. Also the sweathoggs all looked like they were in their late 20's and probably were. You can only suspend disbelief for so long.

When Vinnie and Kotter left, it became a shadow of it's old self.

In addition to that, they made a wholesale change of the writing and producing staff, moved the show from it's familiar timeslot (where it was getting solid ratings) to Monday night and changed focus somewhat to "relevant" storylines about teen issues.

To me, Welcome Back, Kotter boned in the fourth season when Gabe Kaplan and John Travolta were rarely seen. The episodes weren't as funny as the first three seasons.

Vinnie's Departure

Vinnie's Departure

That hurt them really bad.

The irony is that the movie Travolta released during the 4th season, Moment To Moment, was a colossal bomb.