What is the family's Last Name / Surname / Family Name?
The surname of the family was meant to be a secret, but Francis's name tag clearly states "Wilkerson". On the set, however, a comman cast joke was that the surname was "Nolastname". "Nolastname" was used in the final episode (Graduation) on a new name tag for Francis.
There was also a joke that appeared in the original pilot script. In that script, Malcolm was walking to school when a neighborhood kid came running up shouting, "Malcolm, Malcolm, Malcolm. I was talking to my parents last night - I was listening to them talk, and what's your last name?" "Wilkerson, why?" Malcolm replied. "Oh. Who are the Pariahs?" said the other kid. The joke was eventually cut, and the show's writers subsequently decided never to reveal the family's last name, but forgot about Francis's name tag.
Why does everyone call them the Wilkerson's all the time? I realize that was their original name, but it was never once used in the show. We should respect Mr. Boomer's wishes and not refer to them by the name he chose to not call them by. Also, I think one of the highlights of the show is that we don't know their last name, location, Hal's job, etc. It kind of ruins it when everyone calls them by a name anyway. There's even a forum named after their non-existent last name.