Gordon Brown responded to criticism of his "teacher in six months" scheme by insisting that the profession was "higher status" than ever.
In the latest attempt to entice high performers into the classroom, those leaving a successful non-teaching career will be able to achieve professional status in half the current time.
The acting general secretary of the National Union of Teachers, Christine Blower, said that six months' training was "very, very far from being enough".
But the Prime Minister said: "I think it will make a huge difference to the profession and I hope that (despite) initial reservations in the teaching profession, they will welcome the fact that more people want to come into teaching and that teaching is a higher status profession than it has ever been.
"The more people that bring experience from other areas for teaching, the better it is for teaching."
The new training scheme is among the most eye-catching initiatives featured in a new public service reform paper published by the Government.
Ministers are especially keen to attract people with experience in areas such as financial services into shortage subjects like mathematics and science.
But Ms Blower told the BBC Radio 4 Today programme: "It doesn't seem to me to be a sensible idea at all."
