One of the first kids' books that I vividly remember reading. Along with the usual Bobbsey Twins (vaguely), Nancy Drew (had own copies), Hardy Boys (a few) and lots of Alfred Hitchcock collections of stories from the public library (but no Dahl, never came across his books in the school nor public library).
From a 1964 review in the Chicago Tribune (since I can't remember the plot): "A book of spells is un-earthed by a group of the kind of children who live in British storybooks and nowhere else. They turn themselves into cats and mice; they transform as snoopy neighbor into a toad; they fly thru the air with ease and aplomb; they nibble at time travel. But the sorcery is not from Alaric's cauldron. It is in the beautiful, quiet writing, the old cathedral close, the people who need no spells to be enchanted."