The reason there haven't been any mini outbreaks is there are very few children, minimal staff and social distancing adhered to. The problem is that as the number of children increases social distancing goes out the window
I know my daughters primary school only has 8 children attending at the moment and social distancing is working well as I asked the teacher
My DC have been at school throughout, and they are socially distanced in the classroom and at lunchtime. However, they all go out and kick a ball around together, or play in the sandpit, and come hometime all crowd round the door together looking out for their parent. So if you asked our school they'd say they're doing social distancing, and they are, but not all the time.
There have been no instances of covid as far as I know, in staff or pupils. In my DCs school some attend because parents are keyworkers, but more because they are vulnerable, and so possibly not adhering to social distancing etc outside of school: e.g. one family of 5 kids are living between at least 3 homes in varying combinations, sometimes swapping on a daily basis, travelling in cars with adults they don't live with etc, so could be seen as a higher risk. So though there are few kids in school at the moment that doesn't necessarily mean it's going to be more risky when you add in more DC.