Zack's fear of growing up causes him to regress back to childhood when he discovers that he is going to have a Bar Mitzva Celebration at his church. Zack actually transformed back to when 7 years old, and he started acting like a child while Spencer try to figure out how to get the teenage Zack back.
Zack's Bar Mitzva was getting nearer while Zack stayed in school and fooled around, causing trouble for Spence and Cam. Spence needed to make Zack feel more grown up and ready to accept the responsibilities of a boy who is becoming a man.