Averaged across a week, the proportion meeting the guideline rose to 84 per cent; and even in the weekends there had been an increase, to 85 per cent.
The Fonterra free milk scheme is open to all primary schools, of which the co-operative says 1455, around 68 per cent, have signed up. The daily dose of 200ml of low-fat (light-blue) milk is delivered to 140,000 children and virtually all of those in the study who drank the milk said they liked the taste.
"Most children - 73 per cent - reported consuming the milk," said the researcher, Dr Clare Wall.
The weekend increase suggested the children were developing a liking for the taste of milk, she said, and it was hoped the overall increase in consumption would help improve Kiwi kids' health.
"Data suggests children in New Zealand as they grow up drink less milk and less dairy and don't receive the amount of calcium they should.
"We hope that by maintaining or increasing the likelihood of meeting the guidelines, their calcium intake is going to be sustained through critical periods of growth. We hope that affects bone growth and also provides other vitamins and minerals."
She said it had been hoped to run the study with comparison schools not on the milk scheme, but the programme had proved so popular with schools, that hadn't been possible.
Wall's data appears to show there was an increase in obesity, but she said that after adjustments for age there was no statistically significant increase in body mass index (BMI).
"This finding suggests that the Milk for Schools programme was not associated with a negative effect on BMI over a 2-year period."
The study also investigated whether drinking more milk may have affected children's habits in drinking water, sugar fizzy or other beverages, but this data hasn't been analysed yet and may be redundant because of other changes that have occurred.
"Many schools have imposed sugar-sweetened-beverage bans so I'm not sure how meaningful our data is going to be," Wall said.
The study
• Two-plus servings a day of milk or milk products are recommended for children
• Nine primary schools in the daily milk scheme were studied
• 72 per cent of children were consuming the recommended amount at the start of the scheme
• 84 per cent two years later
• 17 per cent relative increase across the two years
Source: Auckland University