They appear to be in an ordinary Argyll jacket with the lapel buttoned across the front. It is possible that the boys weren't wearing "collar and tie" and so the jacket was closed to disguise this fact.

If you look at most jackets today they have a blind button hole on the left lapel. This is a hold over from the days when jackets could be buttoned right up to the collar. Just as the boys in the photo are doing.