This strikes me as being fairly obvious stuff. If someone really isn't up to their job you have to ask if it is right for them to continue doing it, with something as important as the education of children this becomes even more important.
The reaction of the NUT is unsurprising and disappointing. They want to protect the jobs of teachers, that I understand and sympathise with. However, defending underperformance is in itself indefensible.
Things don't get better by accident, if you want to improve thing you have to take action, the NUT need both to understand this and help make it happen.
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