Summer term at St Clare's (by Enid Blyton)

(Amazon UK link) A few months ago I reread ‘The twins at St Clare’s’, the first in Enid Blyton’s St Clare’s school story series. In October I re-read the first sequel, ‘The O’Sullivan twins’. It was at least ten years since I had previously read either of these childhood favourites, and I was quite surprised at how much I enjoyed them. 
It’s more than twenty-five years since I last read the third in the series, 'Summer term at St Clare’s', which I finished reading this morning. I hadn’t remembered...