Some of the stupidest students I taught at the FTU were prior Maintainers.  I've stopped a Crew Chief before from pushing in fuel boost pump circuit breakers because they were popped.  Then I heard that a part of all maintenance school at Sheppard was literally explaining the difference between a Phillips and flathead screw driver.  Just because you were prior [insert job], does not make you successful at a new career field, no matter how much you think you have a one up due to your previous background. 
  
When I was deployed with C-130 maintainers I heard some GAC guy say that Flight Engineers are Maintainers that couldn't hack maintenance.  I laughed, yet he was being serious.