To be clear, the analysis and conclusions are the NFER's alone (though we support them wholeheartedly). SchoolDash's contribution was to providing interactive maps, which hopefully make their results all the more relevant and compelling.
Overall, the results paint a reassuring picture. In particular, high-performing schools outnumber underperforming ones by more than 2:1, and most schools that might benefit from support have one or more high-performing schools nearby (within 2-10 miles).
But not everything is rosy. The proportions of high-performing schools vary greatly by location (see the NFER's interactive map, a screenshot of which is shown below).
For example, they are plentiful in London but much less so in Yorkshire and The Humber, while in certain rural areas, such as in the South West, individual schools are often geographically isolated. Furthermore, in some local authority (LA) areas, schools that might benefit from support outnumber those that could potentially offer it – and a handful of LAs have no high-performing secondary schools at all. Last but not least, even when schools are physically close there might be other barriers to collaboration, such as lack of capacity or incompatibilities in ethos.
Yet the overall thrust of the NFER's analysis is that, to coin a phrase, much of what is wrong with England's education system might be cured by what is right with it. In order for this to happen, though, it must be promoted and supported by government – and expected of schools.
That's our take, but we strongly encourage you to read the NFER's report for yourselves and draw your own conclusions.