"It's like getting blood out of a stone, to be honest," she said.
"I'm not convinced that it is of any benefit."
Matthew, who attends Hillsborough Primary School, spends about 20 minutes a day on his homework.
"I think an hour or so a week is absolutely ample for a primary school child," said Mrs Denby.
Balmoral School associate principal Mary Rea said she saw little value in homework but was pressured by parents to set it.
"We know it's a wasted exercise. But a number of our children will do an hour of learning a night," she said.
Ms Rea said homework should be about learning through participation rather than worksheets.
"We don't call it homework, we call it home learning. What we are wanting is authentic learning situations ... when they help Mum cook dinner they're learning and participating in the process of cooking."
Philip Harding, national president of the Principals' Federation, said there were no national guidelines on homework and many schools were changing their approach.
"Some schools have turned the homework dilemma into child-centred stuff which might involve cooking and a whole range of activities managed by parents, and yet still clearly provide learning opportunities."
Mr Harding said parents should move their focus away from requesting homework and towards encouraging their children to read.
The CensusAtSchool survey found that 69 per cent of teenage students who did homework spent an average of one hour and 13 minutes on it.
Of the teenagers surveyed, 74 per cent of the girls did their homework in contrast to 61 per cent of boys.
Mt Roskill Intermediate principal Mike O'Reilly said homework was a valuable tool to support students' class work.
"Students learn best when they practise what they learn in school and it helps to develop good study habits."
Homework time
Students who did homework the night before
77% aged 6 to 12
69% aged 13-18
Average time on homework
53min: aged 6 to 12
1hr 13min: aged 13 to 18
