top of page

What Do "Wonder Weeks" Or Developmental Leaps have to do with Sleep Training?

I remember when my eldest was a few weeks old a friend of mine told me about this new parenting app that I just “must have.” It was called “The Wonder Weeks” (more on exactly this a bit later – keep reading). The idea behind The Wonder Weeks it is that it will share with you what cognitive and physical skills your child will be learning and using that information to help

predict when baby will be easy going vs when they will be a bit fussier as they make their way through a developmental leap.

A developmental leap is when a baby is learning a new skill. This can cause changes in your child’s behavior and sleep. When babies learn a new skill it takes some time for the brain to organize it and file it away to be used again later. This is how our brains operate.

I loved learning about what my baby was learning in her brain – you know, the stuff I couldn’t not readily observe. Patterns, sequences, colors, depth perception, crossing the mid-line. I loved it.

But when it came to predicting my child’s behavior though it went one of two ways – most of the time it didn’t really help me understand her more (lol) and the other times I used the “stormy” times from the app to make excuses as to why she was not sleeping and any other general fussiness.

And there were nights when she was up and not sleeping (it was rough until about 2.5 years old!) I would think “This is it! I am changing this tomorrow and she will learn how to be a good sleeper!”

Then, sometime in the early morning after my third cup of coffee starts to kick in, I start to second guessing the idea. Maybe I felt like things aren’t that bad yet (after all, it is a “stormy” week!), and I’d start to think something like “I knew what I was getting into when I decided to have a baby,” mindset. I am a grin and bear it kind of person so I did just that.

What are "The Wonder Weeks?"

The Wonder Weeks is something of a Farmer’s Almanac for babies. It was developed by the husband-and-wife team of Frans Plloji, a behavioral scientist, and Hetty van de Rijt, an educational psychologist.

According to the scientists, starting at five weeks old and continuing through the 20-month mark, babies go through 10 mental development stages or “leaps” as the authors refer to them. These leaps, according to the book, take place at very specific points in a baby’s life, starting at five weeks and continuing through the 20-month mark.

“Sunny weeks,” during which baby is typically happy and agreeable are followed by “stormy weeks,” during which baby’s fussy and inconsolable due to the neurological development, and then comes the “wonder week” where the new skill or development is mastered and baby goes back to being “sunny” again.

The Drama

Many, and I mean many parents absolutely swear by this book and its popular companion app. (The original book has sold over 2 million copies across 25 languages.) Some people even claim that it tracks their little one’s development to the day as opposed to the week.

Others will tell you that the science it’s built on is flawed, and that what the authors are doing is essentially a form of pediatric astrology, making vague predictions based on norms and averages, and reassuring its followers that good things are perpetually just over the horizon.

A couple of things to consider for you data-driven types out there. The 1992 study that The Wonder Weeks is founded on, used a sample size of just 15 participants and relied almost exclusively on questionnaires filled in by the mothers as opposed to direct observation from the researchers. Dr. Plooij’s counter argument for the small sample size, stating that if you find a behavior in two individuals, “then you already have proof that the phenomenon exists and is not due to luck or chance,” doesn’t do much to shore up his credibility.

In the mid 1990s, Dr. Plooij’s Ph.D. student, Dr. Carolina de Weerth, attempted to replicate the findings from the original study with an even smaller sample size of four babies, and failed to reach the same conclusions. Dr. de Weerth claims that Plooij pressured her to find correlations that supported his original research, and when she refused, he attempted to prevent the publication of her findings. (A claim that Plooij denies.) Plooij’s contract with the University of Groningen wasn’t renewed following the incident, and he subsequently left academia altogether.

Suffice it to say, there’s still controversy and debate over its legitimacy. But that’s nothing new when it comes to the world of parenting. Is anything ever written in stone when it comes to babies?

Many parents (myself included!) take comfort in being able to predict when their baby will be cranky and that is absolutely fine. If it helps get through a prolonged period of crying to think, “This is just her developing as she’s supposed to,” then high fives all around. Parents need all the support they can get and I say take your mental health boosts where you can find them.

The potential downside I see is that parents might put too much stock in the accuracy of the book or the app, and develop some unnecessary concerns if things don’t go according to schedule. Because if there’s one thing parents don’t need, it’s unrealistic expectations based on inaccurate research, telling them that their little one has failed to hit a developmental milestone on time. You’ve heard me say it time and time again – every baby is different and they are not robots.

So what does this mean when it comes to sleep training?

And that brings us to the reason why I wanted to speak on the whole Wonder Weeks subject today in the first place.

At what point in a baby’s development should you start putting a priority on their sleep?

Is it best to wait until after some of these milestones have been cleared?

If so, which ones? What can happen if we get started too early or too late?

You may have already discovered that your baby is always and consistently going through something – whether it is a “leap” or teething or a regression or a growth spurt, etc. Outside of a diagnosable health issue, there is absolutely no “wrong time” to teach your baby to sleep well.

Right before a “sunny week,” right at the tail end of a “stormy week,” or smack dab in the middle of a “wonder week,” are all perfect times to get the ball rolling. There’s no developmental milestone, no specific week, no time in a baby’s life that could be considered the wrong time to get them sleeping well.


The scientific community and medical professionals are all in agreement that adequate sleep is essential to the health and well-being of everyone in the family unit, and that teaching your baby some independent sleep skills is safe and effective, whether it’s week five or week fifty five.

There are situations where I’ll tell parents to hold off for a few nights, say if they’re going on holiday within a week or so, and I tend to recommend that they get started on a night when they don’t have to work early the next day, as night one can be a little on the turbulent side, but you should never delay your plans to help your baby develop their sleep skills due to some kind of upcoming milestone. Those are going to keep coming, week after week, and your baby will have a happier time progressing through them if they’re getting the sleep they need.

If you are wondering “Ok, great! I’m ready to do this…but wait, now what – how do I actually do this?” These posts may help you.

And if you are overwhelmed (because it IS overwhelming), let’s schedule a call and talk about working together – we can get your family back to sleep in a few weeks!

27 views0 comments


bottom of page