I know we're not supposed to say bossy but they bloody are.
DS has been unhappy on his table all term, 2 boys and 4 girls. One of the girls in particular is very bossy, always pointing out where/how/why DS is wrong or needs correcting. Eg you're not holding your pen correctly, you haven't done enough work, do it this way not that way. Teacher is aware and is aware of um controlling personalities on the table.
It's all came to a head today, DS in tears because the main girl has been on his case all day. Teacher is off sick and there's a sub in the class who has told him to just 'ignore it'.
I've armed DS with saying firmly "you are not the teacher leave me alone" but she just mimicked it back to him 
Any other ideas?