I've read some interesting stuff on brain development already, so I picked up the book to see what else I could learn.
In a nutshell: researchers observed moms and babies for many many years and came to the conclusion that when the babies were 5, 8, 12, 19, 26, 37, 46, 55, 64 and 75 weeks old (or past their due date, when premies were concerned) they grew extra fussy in conjunction with a "mental leap" in how they perceive the world.
So when Olive was 24 weeks old she went through a spat of not sleeping through the night. I posted online about it and someone was like "Oh it's the 26 week leap!" because these leaps can be plus or minus a bit, sure. After about two weeks she was sleeping again. Then she was waking up and someone said "Oh that's because they can re-struggle with week 26 around week 29 because they're coming to terms with the implication..."
The whole thing started to sound like fortune telling to me, no matter what week I was in, someone would tell me it had BEEN FORETOLD. And people who'd read the book looked at every squeak from their babies as self-fulfilling prophecy: "I'm in week 19 and she's crying all the time, I know it's the forth leap it's so awful!"
I found the book itself to have very little to do with the clinical brain research I'd read up on. It was all observational and anecdotal without the hefty list of sources that come with other real books that are based on some science. In fact it even contradicted real science... for instance the book has little sidenotes about gender differences, saying things about how boys will just naturally be more "independent" even though Lise Eliot's very well researched "Pink Brain Blue Brain" details the ways in which our brains develop very much alike. It's our interactions with babies that change how we perceive them: parents throw their boys around more, chat more with their girls, that sort of thing. Baby brains have been studied like crazy for gender differences and nothing much comes out. The only thing that has been confirmed is that we adults definitely treat girl and boy babies differently, interpret their accomplishments and perceive their strengths differently... maybe because we're trying to assign them to little instruction manual boxes. Like this book!
There's a picture at the beginning of the book that looks like a timeline of when your baby may be fussy or not. Half the weeks show fussy. Well that leaves the bases pretty well covered. Do the math on that one people - if week 8 is a "leap" and week 12 is a "leap", and each leap can be off by two weeks, than any fussy time between weeks 9-11 is covered by the prophesy too.
One of the definitions of a medical quack is someone who attributes all success to his own method. The authors of this book have set themselves up quite well for that. It's like jumping in front of a parade, following the route and calling yourself the leader.
There are suggestions to help your baby with their "mental leaps" but I found them to reflect common sense pretty well... things like playing peek-a-boo or showing them their reflections in mirrors.
The book is incredibly easy and cutesy to read and mostly consists of quotes from moms about how trying their various weeks were but oh it was so much easier if I saw it coming thanks to this book.
There are no quotes I could find from dads. The website has exactly zero mentions of the word "father". Apparently only moms are interested in or help with babies.
I'm not debating the fact that babies go through mental development that can stress them. Of course they're learning all kinds of things, brain development is a wonderful thing. But trying to predict it feels stupid. It'd be like trying to predict which weeks a kid will understand more curriculum during the school year based on biorhythms. And who's to even say that every brain examines the same concepts in the same order? Physically, kids mix up milestones all over the place, there's no telling whether a baby will first choose to crawl, sit, sleep through the night. Some babies go straight to crawling without rolling, others go straight to walking without crawling, the point is they all get to some place and we see it but they do it on their own agenda because they are little people and they don't need stupid timeline books.
Babies will go through fussy times, clingy times, silly times, and I really think you should just roll with it. The other brain development book I read brought up how babies are programmed to tell us what they need, and that includes feeding their tiny brains with cool stuff. Babies love to be bounced around because their brain is playing with balance. Their joy in it is a message to us to keep doing it. They love when you hold their little hands and cross their arms so their two sides of their brain have to talk to each other and figure out what's going on. So do that! You don't need a book, just make your kid smile, don't wait for someone to tell you it's the right week. It's not that hard.
So there's my criticism of wonder weeks... popular yes, but trust me, it's worth skipping.
***2016 Update*** Turns out I'm not the only person who questioned the science of this book! The author's own grad student tried to verify what it was saying with an actual study and oh dear, nothing claimed by the book could be duplicated. Science FTW! And I'd like to thank Wikipedia for being a good source of sources, connecting some of these dots worth connecting, telling the story, as it does best.