That's an interesting question. It almost presumes an either/or, and I don't see it that way.
I see children in schools working with staff and caterers within a set of constraints, because at the moment what we have.... We may want to get into this when we're looking at things such as vending, snacking, the impact of advertising, and the large companies.
I've seen the disgraceful development of large multinational soft drink and confectionery companies taking over, as they did in the United States, the whole of the vending/snacking operation and making a very considerable profit. In effect, they were buying profits at the cost of poor health to the children.
Quite clearly, there was an easily understood cynicism or, if you like, an inconsistency between teaching the importance of fresh fruit and vegetables and a balanced diet in the classroom and then selling high-fat, sugar-laden soft drinks and confectionery throughout the school.
It doesn't add up. So it seems to me that you establish a pattern of best practice, good quality catering, and good quality other services, such as vending and snacking. Then within that parameter, you sit down with your children and your caterers to say okay, how do we deliver these changes? What is the best way to operate? What's the time scale, and what level of flexibility is there for negotiations?