"It's a continuum," he says, "so the effects are reduced, but they are not insubstantial. Another way of looking at it is that monolingualism is an educational disadvantage. With any language-learning, particularly as you become more proficient, those advantages accrue exponentially."
These benefits accrue irrespective of the language learned, May says. French, Mandarin, Xhosa all do the job. So in Te Wiki o te Reo Maori, or Maori Language Week as it is known in English, it's apt to consider what the logical choice of language might be in New Zealand.
In doing so, it's worth remembering that all this talk about how our kids should learn Mandarin or Spanish because they are more "relevant" to our economic future is bollocks.
No one ever left school having learned, at school alone, enough of any language to do trade talks or diplomatic negotiations. The point of language-learning at school is not the language, it's the learning.
The level 3 and 4 kids in Room 10 at Windy Ridge School in Glenfield, who welcomed me into their classroom on Monday morning, have had barely half a dozen half-hour sessions with kaiawhina reo (language assistant) Keri Hadfield (Ngapuhi/Te Aupouri).
But they've got colours, numbers and days of the week down pat. They know a bunch of prepositions (runga is above; raro below) and they sing the waiata with all their might.
"I like it when whaea Keri comes," one kid says to principal Brenda McPherson as she settles them down and announces Hadfield's impending arrival. "She's nice," she says, adding after a moment's thought, "but not as nice as you".
As Hadfield puts the kids through their paces, it's plain that they are loving every minute of it.
"I like learning new words," says one, when I ask what is good about the classes. "It's good to find out about different cultures," says another.
A jaded mind might suspect these endorsements were rehearsed, but the kids are right. The idea that the structure of a language dictates the way its users see the world arose in the late 19th century and was so widely accepted by linguists in the mid-20th century that it is now a truism.
If you don't think it's useful to learn something about how others see the world - particularly when those "others" are the first colonisers of this land - you presumably don't believe in education at all.
The Labour Party has been anxious in the past few days to distance itself from the claim by the Maori Party's Te Tai Tokerau candidate, Te Hira Paenga, that it had endorsed his party's policy for making te reo classes compulsory in primary schools.
Windy Ridge's Brenda McPherson doesn't like using the c-word, either, because she is conscious that it raises the hackles of those who detect some sort of social engineering - an idea that would be laughable if it were not so bleakly ironic.
At Windy Ridge, one of a couple of dozen North Shore schools that this year implemented a programme called Te Reo Tuatahi, they prefer to see it as simply something that they do. Of the 5000 children involved in learning te reo, McPherson knows of just one whose parents questioned the wisdom of the programme. The parents were new immigrants and quickly accepted the idea when its virtues were explained.
It's worth adding that the programme, taught by fluent speakers under the supervision of the class teacher, takes only half an hour a week. Each year, it gets a little harder to see how you can argue with that.
