<p>I’m not reading it quite so literally as you. I might think of this in tiers with A+ being Tier 1, A being Tier 2 and so on with the ultimate conclusion being that the differences from one tier to the next aren’t sharp. But the argument for moving a school up or down 2 tiers is a more difficult proposition. </p>
<p>The fact that you’re struggling to find a bright line is not a bad thing. IMO, using something like CP as a source should provoke inquiry rather provide conclusive answers. After all, it is an opinion survey and people will sometime reach different conclusions.</p>