Apprentice teaching assistants, some as young as 16, could take classes of pupils just two years younger than them, ministers confirmed this week.
Schools minister Jim Knight said the apprentices in secondaries should be "encouraged". "We would want to see apprentices working in school offices, in the grounds and in school kitchens," he said.
"You could have teaching assistants working perhaps with key stage 3 rather than KS5."
The news followed Ed Balls's call for greater take-up of the apprentice scheme from the public sector. The Schools Secretary told a Commons select committee he would like to see 4,000 apprentice teaching assistants in schools in the next year.
After the meeting, he said: "We can't require schools to do this - it is something for individual schools to consider. But I think we could have 4,000 of the 35,000 apprenticeships in schools or early years."
But the NUT criticised the idea, saying it would not endear Mr Balls to teaching assistants. The teaching union's acting general secretary, Christine Blower, said: "This is an ill thought out idea. There is plenty of scope for work experience in schools, but not apprenticeships.
"Schools are already hard pushed to cover all the work that needs to be done...
"There is not the capacity for monitoring such a scheme. Teachers need assistance in the classroom, but having to assist apprentices in the classroom will pose too much of a distraction from their core responsibilities."