James Bunn believes his working week is two hours shorter thanks to the workload agreement.
Mr Bunn, head of physics at Moulsham high school, in Chelmsford, Essex, says new clerical support has cut by half his administrative work.
Since September, the school has taken on four part-time departmental assistants, so all of the 1,500-pupil comprehensive's 18 departments now get help with work such as data entry and putting up classroom displays.
Mr Bunn, 32, said that teachers at his school had already stopped doing many of the 20 routine tasks identified in the agreement - such as collecting money - before September. But now there is extra support: the admin team provide about a day's help a week to the science department. Mr Bunn no longer has to chase absent pupils. Much filing and photocopying is now also done for him.
But he is not completely free of all routine tasks. Some, such as setting up displays, he said he took pride in doing himself.
It took time for the admin team to make a difference as they learnt their new roles. But he said: "Now we're seeing a dramatic improvement, not only in terms of doing less admin: we are more organised, for example in the data we keep on students' work and the resources we offer them."
The other major change has been for Moulsham to take on two new non-teaching assistant heads of the lower and middle schools. They are on call should teachers have problems with behaviour, or parents ring in urgently needing to speak to a staff member.
Valerie Whitehead, who leads the administrative team, said most teachers welcomed it. "But others say they would rather do the work themselves, to ensure it's done properly. I think the longer we are here, the more that will change."