Best Friend(s) - title, I think, children's book. I read it about 1960. 3-6th grade reading. Girl's mom is her schoolteacher and she gets called teacher's pet. Grandfather lives with them and she has a great tree house. Half-French girl moves in next door and they become best friends. Archenemy is Millicent. End of story the girls get "matching" puppies. Remembering where it was in library, the author's name began with A-H. Hardcover, minimal illustrations. I think the phrase, "no more sense of time than a cricket" was used.