Then

The Milk in Schools programme started in Auckland, Christchurch, Wellington and Dunedin on March 1st 1937.
The first Labour Government of New Zealand introduced the milk programme because children were not getting enough calcium in their diet.
The milk used was pasteurised to kill off microorganisms which would cause spoilage and to extend the shelf life. The milk was then put into sterilised bottles.
The bottles were made of glass and were a half pint (similar to a 300ml bottle of cream).
The first milk bottles had cardboard tops with a small whole for a straw. Children used to use these cardboard tops to make pompoms. Later the tops were made of tinfoil.

The local milkman would deliver the milk early in the morning to school in his truck. The bottles were carried in grates made of wood, wire or plastic. Each grate carried about 20 milk bottles.
The milk was left at the school gate in a large concrete shelter.
School milk monitors would take the grates from the gate and leave them outside the classrooms where they could sit for several hours before the milk was drunk.
Lots of children thought the milk tasted yuck because it was warm and sometimes curdled. Drinking school milk was compulsory and sometimes the milk made the children throw up.

In some schools the milk monitors had the job of washing out the milk bottles before the empties were put back into the grates and left in the concrete shelter for the milkman to pick up.
The programme lasted for 30 years. It was stopped in 1967 because the government said it cost too much and some people doubted the benefits of milk.

Auckland school children drinking the daily issue of free milk. Making New Zealand :Negatives and prints from the Making New Zealand Centennial collection. Ref: MNZ-2461-1/4-F. Alexander Turnbull Library, Wellington, New Zealand. http://natlib.govt.nz/records/22567578

Schoolboys in Linwood, Christchurch, carrying crates of milk. Pascoe, John Dobree, 1908-1972 :Photographic albums, prints and negatives. Ref: 1/4-000030-F. Alexander Turnbull Library, Wellington, New Zealand. http://natlib.govt.nz/records/23185540

Two primary school girls drinking their school milk, Linwood, Christchurch. Pascoe, John Dobree, 1908-1972 :Photographic albums, prints and negatives. Ref: 1/4-000032-F. Alexander Turnbull Library, Wellington, New Zealand. http://natlib.govt.nz/records/23196181