"We know that if kids eat and drink well, there are a myriad of benefits and good outcomes for learning.
"The Government wants to ask what people think about all primary schools offering only healthy drinks, these being water, milk and non-dairy milk alternatives, to their students."
Some schools had already put their own healthy drinks policies in place, including water-only policies that permitted only water and plain, low-fat milk.
Act's education spokesman Chris Baillie said the policy was a case of "control freak politicians... taking over the job parents used to be expected to do".
He doubted the policy would work.
"Any good parent knows that when you ban something, it only makes kids want it more. Instead of getting a drink from the canteen, they'll simply head to the dairy up the road to buy their Coke," Baillie said, adding that Act reckoned schools should be allowed to decide what to offer students.
The proposal was initially only for primary schools but the Government is considering a similar policy for secondary schools.
"Promoting healthy food and drink in schools is common practice in other OECD countries. Evidence also shows the earlier in a child's development that healthy habits can be encouraged, the better."
The consultation is being run by the Ministry of Education and closes on June 2.