Betsy and Tacy Go Over the Big Hill
(1942) is the third volume in the Betsy-Tacy
series by Maud Hart Lovelace
While the first two volumes are something like collections of vignettes about Betsy, Tacy, and Tib, this one has a story through the whole volume. The girls are competing with Betsy's and Tacy's older sisters about having a Queen of Summer. When they go out to collect votes, they find themselves making friends with a surprising little girl their own age in the Little Syria section of Deep Valley.
Betsy and Tacy first sing their "Cat Duet" at the school entertainment in this book.