At the beginning of this episode Zack said it was the first day of school but his mom told him that he needed to stay home and rest. But the first day of school of this Season was in the episode "The Fight".
It seems a little hard to believe that a high school principal would be sending all these kids over to Zack's house to check up on him. If Belding had his doubts, it seems he would just immediately go over himself, or contact Zack's parents. No one is going to keep sending students off campus. If anything had happened to any of them while they were going back and forth, Belding would have had a lot to answer for and almost certainly would have been fired.
At the end of "The Last Weekend" episode, Zack and Stacy were together. This episode was supposed to be a continuation of that episode, but Zack speaks nothing about missing her or anything about Stacy.
Slater: Tell her I'll think about it.
Zack: Jessie said "Once a pig always a pig."
Slater: That's my mama.
Belding isn't in the episode, either, although there a number of references to him.
Neither Kelly nor Jessie are in this episode, but they are mentioned and Zack gets a "call" from them.