After Jessie leaves the Max mad at Slater, Kelly goes after her. Just before Kelly leaves, someone runs past the door by the backdrop.
When Zack and Screech are talking to Moose at the Max, you can see a set light at the very top of the screen.
No explanation is given for why Nicki is hanging around a High School when she should be in Middle School.
When Jessie calls the teen line, the boom mic is momentarily visible above Zack and Lisa's heads.
At the beginning of the scene where Lisa starts helping Slater and Jessie, the boom mic is seen for a split second.
Zack calculates that he and Screech will get rich because each phone call will net them $2 and they will answer calls for five hours a day. However, they do not know how many calls they will get per day and did not factor in the expenses of the phone lines so they would not be able to accurately estimate how much of a profit they may see from this venture.