The Wonder Weeks is a baby guidebook turned baby-advice juggernaut that offers parents the promise of being able to predict and exploit a series of developmental leaps over the first two years of life. That promise is laid out in the book’s subtitle: How to Stimulate Your Baby’s Mental Development and Help Him Turn His 10 Predictable, Great, Fussy Phases Into Magical Leaps Forward. For over 27 years, parents have continued to be hungry to stimulate those magic leaps. The Wonder Weeks has been reprinted multiple times since its debut in 1992 and spawned a baby-advice media empire that includes apps, an online course, and emailed “leap alerts.” Even Pampers leveraged The Wonder Weeks to give parents insight while using their new smart diaper.

As a parenting franchise, The Wonder Weeks clearly has staying power and unrelenting influence. But there’s a problem: The guide’s vision of child development is more convenient construction than scientific fact. Moreover, the man who developed The Wonder Weeks, Dr. Frans X. Plooij, has shielded his book from all sorts of questions surrounding the veracity of the underlying theory. He even went so far as to attempt to stop the publication of a study that challenged his work before he left academia.

What is there to hide?

The core of the idea is that children progress through 10 distinct phases of developmental “leaps” — the proverbial wonder weeks — that occur on a predictable timeline. These phases are preceded by a period of general inconsolable fussiness and followed by a period of general happiness. The trick is that if parents know that the fussiness is preceding a cognitive leap forward, they can promote a calm transition by helping their baby develop the interests and abilities distinct to that stage.

In a way, The Wonder Weeks place a new spin on the idea of developmental milestones. The difference is that the leaps within this theory are linked to neurological development and are supposedly more acute and predictable. This is where the cracks start to show.

Baby development occurs on a continuum rather than a fixed schedule. Moreover, every child is different. Babies will develop their abilities at their own natural pace and rhythm based on myriad factors including their genetics, their diet, their environment, and the adults who interact with them. So, the milestone of rolling over might occur at 5 months, but that’s an average. It could also happen at 4 months, or 6 months. To suggest that babies will experience a mental leap that profoundly changes the perception of their world at distinct and precise intervals isn’t supported by the bulk of research into infant development.

“Most claims about discreet stages turn out to not hold up,” says Dr. Celeste Kidd, a baby development researcher with the UC Berkley Kidd Lab. “Most kinds of cognitive development are not sitting in a silo.”

Kidd notes that developmental psychologist Jean Piaget is responsible for the idea of cognitive development occurring in stages, but notes he did not intend for those stages to be considered as discreet. In fact, some behaviors linked with different developmental stages can be occurring simultaneously in the same kid. In other words, like most things associated with babyhood, development is messy.

“Stages are a useful shorthand for describing a theory of how development works when actually the real dynamics are complex,” Kidd says.

And that’s likely why Dr. Plooij hoped to find the distinct pattern of leaps he describes. Being able to map a baby’s mental development as magic leaps would be incredibly helpful, particularly if it could explain infant fussiness. But when Plooij’s Ph.D. student attempted to replicate his findings she was unable to find evidence of the leaps. Plooij was vocal in criticizing his student’s study, titled “Emotional instability as an indicator of strictly timed infantile developmental transitions,” and attempted to keep it from being published. The controversy ultimately led Plooij to lose his place in academia.

This is not to say there’s no value in The Wonder Weeks or that this is in any way a dangerous book. The book lays out a general roadmap of infant development in a most accurate and extremely helpful way. In other words, the way it organizes information about baby development is helpful when considered in a broad scope. And the stages described in the book capture enough of the average baby experience that many parents will see their child reflected in the text.

Clearly, this is deeply comforting to parents. It gives a sense of control and understanding. The Wonder Weeks also gives parents something to do, even if what they are doing is not accomplishing the intended outcome — reducing fussiness and helping specific leaps occur.

“People are really good at seeing patterns. Fussiness can be driven by any number of things,” Kidd says. “It can be tiredness; it can be frustration; it can be a headache. It’s really hard just given one signal to draw one conclusion about what the cause is. It’s a comforting thought, but it would be difficult to know if that were true.”

Still, The Wonder Weeks feels true. It has, after all, garnered thousands of testimonials from parents who begin to interact in the prescribed manner and see fussiness decrease. This too may have a simple coincidence that isn’t the intended magic.

“We have tons of evidence to suggest that kids like when they are being attended to. And kids like being responded to,” Kidd says. “They like when they make requests and they are answered. They learn better in those circumstances.”

What makes Wonder Weeks so popular, helpful, and influential has nothing to do with any specific research or insight gleaned by its creator. Here’s how it really works:

• The book offers a broad general description of average baby behavior during early development.
• Parents of typical babies see their child reflected in the average and feel empowered by a perceived ability to predict developmental leaps.
• Parents feel comfort from believing generalized fussiness is related to important developmental work the baby is doing.
• Parents engage in prescribed developmental activities and the fussiness decreases due to parental attention and consideration.
• Parents feel that the baby has progressed through a leap and feel better about themselves, their baby, and most importantly, the book.

Importantly, none of the magic attributed to the book actually requires purchasing The Wonder Weeks book or downloading the Wonder Weeks app. It just requires paying attention to a baby’s cues and providing them positive, happy attention, and interesting play. The book isn’t harmful, just unnecessary.

Of course, in some circumstances, the book can be very unhelpful. A baby affected by congenital birth defects or developmental delays, for instance, may develop on a much slower timeline. The same goes for babies affected by poverty or toxic environments. Other babies may simply progress at their own pace, leaving parents frustrated and even more anxious that their child is not following the book.

But Kidd notes that there is a way for anxious parents to find accurate and scientifically sound help.

“Talk to a pediatrician,” Kidd says. “They are great at talking parents down. They have no incentive to BS you.”

The same can’t be said for Dr. Plooij.

This article was originally published on Aug. 30, 2019