Reagan Dale Neis, who plays Malcolm's schoolmate and girlfriend is actually 9 years older than Frankie Muniz in real life
Malcom's girlfriend (Reagan Dale Neis) also appears as Laura in the season 2 episode Evacuation
The big kid with the nice car that Dewey wrecks is Ira from "Reese's Apartment". In both episodes he has the persona of a football player, indicated by his letter jacket in this episode
Michael Shamus Wiley (Nikki's father) also played a recurring role in Breaking Bad with Bryan Cranston as the head of the DEA office.