Did you notice that the chap front row second from the right is wearing a pinky ring? Possibly the one far left front is as well. I assume this means they are well to do? (They look it) 
.....
In NZ these are called signet rings and are not the preserve only of the wealthy and not only for men. While my dad did not wear one or any ring, some of his cousins/brothers did and sisters/girls also got signet rings around 13 years, as I did. These were worn either on the little finger or third finger on the right hand.
At the time there were not the extreme of class/e wealth in NZ as there are now. There was a large what you'd call now, struggling middle class or lower MC from the 1920s on and these look as though they would be contemporaries, including immaculate dress, of my Dad's.
Most secondary schools both public and private had army training schemes/territorials, boarding establishments and many of the first volunteers were from this background. My Dad drove 60 miles to the nearest recruiting centre the day after war was declared to volunteer but was held back as he occupation as Secretary of a dairy factory was held to be essential. He was overseas a year later.
I think you'd find that these men were well educated, ATC trained and I guess they themselves would be hesitant in assigning themselves to a class. It was generally not a thing and was a point of pride and difference here in the 'colonies'....
