Let's take supermarket workers, as an example. Yes, the guidance says that they should stay 1m apart from the other people in the supermarkets at all times. But we all can see with our own eyes when we enter a supermarket that it isn't always possible. When they are at the till they are behind a screen. But when they are stacking shelves they are not. They have a lot more touch points than a teacher would have. They have contact with very many more people than a teacher will have. Yes, they may be able to stay 1m apart from most people more of a time than a teacher will, but if you balance that out with the increased number of people that they come into contact with, and their increased touch points, is their risk less?
Sigh. Maybe just read up a bit on how this virus spreads? The issue is not how many people you come into contact with - or we would have seen massive rises in the stats following VE day or the beach trips of late. The issue is how a virus moves through an enclosed space with a blow it all about heating system and poor/no ventilation vs. time spent in that space. The science of it is saying 50 minutes in a room with someone who has the virus is enough to infect others. This is why public transport is an issue with proximity and closed spaces - hence bus drivers having a high death rate, hence taxi drivers having a high death rate.
And then there's 1000 plus students charging through narrow corridors, deliberately coughing on people, not washing their hands no matter how many times you tell them to. In primary, students have less concept of personal space and some will need personal care. Staff have to manage, for example, injections for type 1 diabetics. Handwashing is, at best, patchy.
At least supermarket workers are afforded some protection - many are wearing masks, their clients are wearing masks, most people are trying to keep the distance, they have the perspex protection at tills. Their contact with someone with the virus is likely to be seconds/minutes, not 6 hours. More importantly, adults as a whole understand personal space way better than 6 year olds.
I don't know who is most at risk statistically, but I would rather be in a supermarket right now than in a school based on everything I have read.