Character mistake: Brandon begins the scene giving his speech while he is sitting/leaning on the desk. The students all move into the picture from both sides and gather around Brandon then they all say, "There's no hope with dope". After the conversation with Mr. Belding, they watch the commercial they just shot (beginning with each student giving his/her opinion about drugs). Then Zach says his speech while sitting/leaning on the desk. He stands up, the rest of the students and Brandon move in and gather around Zach, then Brandon gives his anti-drug speech.
Character mistake: Lisa is upset about being paired up with Screech. Mr. Belding explains to Lisa that the matches were paired up alphabetically. But this is proven incorrect - although Kapowsky (Kelly) and Morris (Zack) are very close, and Slater (AC) and Spano (Jessie) are even closer alphabetically, Powers (Screech) and Turtle (Lisa) should not have been paired. Assuming no other kids names' interfered with these six (in which case the groups would be different anyway). The correct pairs would be Kelly and Zack, Screech and Jessie, then AC and Lisa according to true alphabetical order last names.
Character mistake: While holding the fake raffle, Zack says Mr. Belding won't be back for two days. Mr. Belding shows up suddenly, surprising the boys that he's back early - however, at the end of the scene, Slater says to Belding, "we weren't expecting you back til tomorrow."