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What is all the fuss about the Wonder Weeks?

The Wonder Weeks is one of the most popular books and apps for tracking baby’s cranky phases and mental “leaps” forward, but here’s why you should only take it with a grain of salt.

What is all the fuss about the Wonder Weeks?

Photo: iStock Photo

Google “Why is my baby crying?” and you’ll get millions of responses (no, really, there are 183 million at the moment) that try to answer the one question that every single parent asks. Surprisingly, there’s a very popular theory that doesn’t point a finger at the usual suspects: being hungry, having colic or gas pain, being too hot or too cold, wanting to be held, feeling too sleepy or overstimulated, having a dirty diaper or thinking you had the nerve to sit down while rocking. The theory not only suggests that there there is a simple reason for incessant crying but also claims that baby’s fussiness is a good thing and part of their development. Say what?

What is The Wonder Weeks, and how does it work?

The concept of The Wonder Weeks was developed by a Dutch husband-and-wife team, Frans Plooij and Hetty van de Rijt, 40 years ago. Plooij is a behavioural scientist who studied mother-and-baby interactions, mostly in chimpanzees, and Van de Rijt studied educational psychology, as well as infant development in chimpanzees. They published The Wonder Weeks in 1992, and in the book they describe how babies go through mental developmental phases, or “mental leaps,” that help them build awareness of the world around them. Since these stages often cause little ones to regress and experience frustration (everything is so strange and new in their world), they can be irritable, anxious (hello, clinginess!) and miserable.

The doctors discovered 10 predictable mental leaps that are tied to age, from the time an infant is five weeks old to the 20-month mark. They coined the term “Wonder Weeks” to describe how specific weeks of a baby’s life correspond to those leaps (these leaps are just like the growth spurts that wee ones have for physical development). Here’s how it works: Babies have a “sunny week” (when all is peachy), which is followed by a stormy week (lasting one to four weeks). Then a Wonder Week hits and—poof—the baby meets a developmental milestone. The schedule of when and what to expect gives parents intel—the idea is that we can anticipate these changes and stimulate our kids’ senses by feeding into their development when they reach certain weeks, as well as help them feel less frustrated. The experts don’t call it parenting advice per se but rather “baby insight” that can help arm moms and dads with the knowledge to help them get through those early trying times.

It may sound pretty good when you think of Wonder Weeks this way—you can finally stop blaming yourself for your perceived lack of parenting prowess when you have a crier on your hands. It’s not you; it’s them. (Seriously.) And the sometimes-inconsolable bawling shouldn’t bum you out: “The difficult behaviour is actually a signal that great progress is underway,” says The Wonder Weeks site.

How can you follow The Wonder Weeks?

You can buy the bestselling book (it’s been updated and revised over the years) or get the wildly popular app (go ahead and peruse through comments on iTunes—there are thousands) for all the details, but here’s a sample. The second mental leap occurs in Wonder Week 8, and it’s all about your baby discovering their hands and feet. This significant development allows them to kick their legs and swing their arms. The sixth mental leap happens in Wonder Week 37 (around the ninth month) and has babies jumping into the world of categories—a development that’s marked by tots recognizing the differences between objects and investigating how they’re different. They will also start to categorize objects: Bananas and spinach look, taste, smell and feel different, but they’re both foods. In each leap, there are tips on ways to stimulate your baby, reasons why they get fussy and what to look forward to after a milestone is met. 

What do other experts think of The Wonder Weeks?

Meta van den Heuvel, a social paediatrician at Toronto’s Hospital for Sick Children, was trained in the Netherlands and is familiar with the Wonder Weeks concept, but she doesn’t use it. However, she lauds it for the reassurance that it gives parents that all babies get fussy and cry. “It also offers appropriate things to do with babies at different stages, such as ways to give attention, toys to play with, music to listen to and the importance of reading and cuddling,” she says. But the problem with parents taking Wonder Weeks as gospel, says Van den Heuvel, is that there isn’t enough evidence to back it up, particularly with observational trials on human babies as opposed to chimps.

Actually, there’s some controversy around this. One of Plooij’s doctorate students conducted her own research, looking for evidence of the so-called “leaps” in infants, and found none. When she attempted to refute the concept, Plooij tried to block her work from publication and much debate followed. Plooij ended up getting fired from his teaching post and left academia.


If you’re already not sold on Wonder Weeks, this won’t sway you—experts like Van den Huevel say that the screening tool doesn’t take risk factors (such as premature babies, kids born with low birthweight and other genetic information) into consideration. Even the parents of babies who develop typically may not realize that there’s actually a fairly big window when it comes to what’s considered “normal development.” And if you’re, well, like us, it may even cause needless worry if your kiddo isn’t meeting expected leaps right on schedule.

Should you worry if your baby isn’t on the Wonder Weeks schedule?

The Canadian Task Force on Preventive Health Care takes a similar stance. Its research into screening for developmental delays in one- to four-year-old kids was published in the Canadian Medical Association Journal in 2016. While the researchers didn’t specifically look at Wonder Weeks, they studied other tools and found no evidence to suggest that screening for developmental delays in toddlers (who didn’t have developmental concerns) improved health outcomes. The findings led the task force to speak out against screening for developmental delays using standardized tools. “Screening tests have poor to moderate accuracy, and their use generates a high number of false positives in children without developmental delays, which could lead to anxiety,” according to the task force.

Van den Heuvel agrees that the concept of developmental milestones may cause parents to feel like their babies aren’t developing “normally.” “In general, it’s important not to be too rigid,” she says. “My perspective is that fussiness and unusual crying can be the result of several things, such as constipation or the need for attention, not just because it’s week 10 and something is supposed to happen at exactly that time. It’s not firmly predictable.” Referring to  The Wonder Weeks app that has an alarm to notify parents when their baby is due to make a leap, she adds, “Development doesn’t work like that—you can’t say ‘This is going to happen on this day.’”

If you’re looking at books and tools like these, don’t take everything you read to heart, adds Van den Heuvel. “Parents should trust their instincts and talk to their child’s paediatrician if they have concerns about their development,” she says.

If there’s one thing that these tools are good for (besides giving parents ideas about ways to engage their kids), it’s using them to guide conversations between parents and healthcare providers. If you notice that your 15-month-old isn’t saying much and doesn’t have the exact number of words they’re supposed to have mastered at this stage, according to whichever tool you follow, take the opportunity to bring up your concern and discuss it with your child’s physician. You’ll feel much better knowing that your tot is on the right track, whether or not an app says so.


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