Just as they start having to do some actual work
Nothing aginast teachers in general, just those that choose it as a career path then moan about pay and conditions that are well published beforehand, you know the kind, those who prove the occational rule, those who can't; teach.
Then you get those who do enjoy their work and will rarely go on strike as a result, while also actually doing a much better job than those who went into it 'for the money'.
When TeachFirst tried to recruit me into teaching with a stand in the George Begg Building they where quickly told where to shove it, advertising salary benifits etc. They can still sod off, I'm not teaching at this age... (Used to instruct 13 - 18 year olds so I do know what it's like.)