That's a in interesting read (although I've only skimmed it TBH) but it's from Independent SAGE rather than SAGE.
It would seem like common sense to only open in areas with less current infection though. Something like that will probably happen, although in the absence of proper tracing the decisions will probably be taken more on political grounds.
Something that reduces the risk of opening the schools is that loads of parents won't be sending their kids in. I've got a reception kid and loads of the other parents are not at all keen. We are in London and think that there is only a relatively low level of the virus here right now (we have a friend who works in ICU at local hospital) so are all for it.
We're not exactly sure how it will work (if it even goes ahead on Monday) but are expecting the reception classes of 30 to be split in half doing half-days. With low attendance, it's likely the classes will only have 7-10 kids.