This was part of the reason for the "No child left behind" act from President Bush. There are many many schools using teachers for subjects they didn't go to college for... But that's a whole different discussion.
In my 11th grade we had a math teacher teaching our computer science class... He didn't know a whole lot about computers and all of us just played Quake 2 or Worms Armageddon. Its a shame that this happens but what else can you do when you have a shortage of teachers? Now if this shop class was something the teacher elected to teach and knows they can get out of it by having a competent student doing all the work