I'm a fan of Streatfeild's /Shoes/ books from way back: I had Ballet and Movie when I was a kid in the 80s, and have read a few more since then. This book is different from any of the others. In general, Streatfeild is pretty gentle with her protagonists. While a character might be grouchy and untalented (cf Jane in /Movie Shoes/) the author still grants that child with some saving graces. Not so Peter and Santa, the orphans of /Circus Shoes/. Due to their being raised by an idiot aunt, they have reached the ages of 11 and 12 as complete idiots, a fact that Streatfeild points out several times per chapter. There is something sadly hilarious about how stupid and talentless these kids are. They have nothing--literally, nothing--besides their love for each other. They suck at school and lack any sort of street smarts. They have no physical abilities; 12-year-old Peter literally cannot catch a slow lob. They have trouble relating to other human beings all of whom, they've been taught, are beneath them. They are colossal snobs, a trait that shines through in everything they do, including how they dress, talk, and walk. In short, they are practically irredeemable. But Streatfeild is not as cruel as all that: she kills the idiot aunt and sends Peter and Santa to the one atmosphere that could possibly kick them into shape.
When they go "tenting" with their uncle Gus, a true "artiste," they learn the values of circus folk: hard work and more hard work. Pride is taken only in perfect accomplishment. Everyone is equal, and no one is grander than anyone else. Most importantly, the circus people tell Peter and Santa, in no uncertain terms, the things they need to hear, that they are, in fact, idiots. However, they are not inherently idiots. Only the idiotic things they learned from their aunt make them stupid, and correspondingly, if they choose to open their minds, they can learn not to be idiots.
For a kids' book, it's pretty long, because Streatfeild shows Peter and Santa learning everything there is to know about big top life. There are pages and pages dedicated to putting up and taking down the big top. Even more space is dedicated to animal training and psychology, along with some good discussions of various types of acrobatics. And of course, we also see the performances through Peter and Santa's eyes: the first time they ever see the circus, and then, later, when they've learned something about it, more in depth understanding of the art.
Despite their obvious deficiencies, the reader is constantly rooting for the kids. Not, as in the other Shoes books, for the kids to achieve the professional artistic success toward which they have worked for so long, but simply for the kids to join the human race. When Peter learns to ride a horse, it's a great relief, because it's troubling he literally cannot do anything else and, as a reader, you don't want to believe that he's that useless. When Santa learns that she must practice with a will in order to become a true performer, it's a fitting cap to end the softness that characterizes her life up until that point. We're talking about a kid who takes almost 200 pages to realize that she can braid her hair to keep it out of her face.
The only possible ending to this story is for Peter and Santa to transform, completely, in circus performers, but Streatfeild, as she does, saves this climax for the very, very, very ending of the book (there's no denouement), nearly breaking the reader's heart as s/he contemplates how badly Peter and Santa will suck at anything else they set their hands to.