Family sitcoms from the 1980s were big on teaching lessons.
Small Wonder, for example, had quite a few such episodes. These two come to mind.
In the first-season episode, "The Lie", Jamie Lawson (Vicki the Robot's human "brother"), as it says on the cover of the DVD (yes, I bought the DVDs since I love this show so much, but that's another thread), "learns the value of consistent honesty when he can't convince his parents [Ted and Joan] that he's not responsible for breaking a teapot." For those who remember, it was actually the cousin of next-door neighbor Harriet Brindle (you know, the girl with the pigtails who thought that she was destined to marry Jamie) who actually broke the teapot. But because of all the previous things that Jamie lied to his parents about, they didn't believe him--that is, until Vicki bailed him out with her built in tape recorder. On that recording, was Harriet's cousin's confession. So Jamie got no further punishment from his parents for that offense.
In the second-season episode, "Victor Vicki-toria", Jamie is on a baseball team with his best friend Reggie Williams and Jamie asks the coach if Vicki can be on the team, but there is a "no girls allowed" policy. So Jamie comes up with a crafty plan--to dress Vicki up as a boy and pass her off as his cousin, Victor. (You may recall Vicki's superhuman strength seen in many episodes, such as lifting heavy objects with one hand, such as a bed or an easy chair or what have you. The superhuman strength was the reason for Jamie to do this, since his team was in last place.) Ted and Joan, of course, are against this idea, calling it cheating. So, Jamie decides that his parents are right, and on the field, Jamie then goes to the mound and verbally programs (she's not called a Voice Input Child Identicant for nothing) Vicki (still in drag as Victor) to imitate Ted throwing out a muscle after throwing his "Fernando ball" earlier in the episode
Full House is no stranger to morality plays, either.
There was one episode (along those same guilty-until-proven-innocent lines as the first SW episode I mentioned above; actually, the SW episode would probably be a combination of boy-who-cried-wolf and guilty-until-proven-innocent) where D.J. Tanner smells like alcohol after the stuff spilled on her clothes, Danny Tanner punishes her for underage drinking because he thought she was lying about it. It turns out she was telling the truth. Danny eventually apologizes to D.J. for not believing her. So in this case, parents can learn from this type of episode, as well. That lesson being to back up your accusations with facts and not try to trap someone in a lie if you don't know whether the person is telling one or not. Otherwise, you'll be the one who looks bad.
Do the above TV episodes count for this thread?