The Wonder Weeks by Frans X. Plooij: A Deep Dive Review

Categories:

A review from someone who desperately googled “why is my baby suddenly possessed” at 3am and discovered there might actually be an explanation—and a predictable schedule for the possession

Your baby was perfect. Sleeping well. Eating well. Smiling at everyone. You thought you’d figured this out.

Then, without warning, they became a different baby. Clingy. Fussy. Waking constantly. Refusing to be put down. Crying for no apparent reason. Rejecting the breast. Rejecting the bottle. Rejecting everything except being held while you bounce on a yoga ball in a dark bathroom with the fan running.

You check for fever. You check for ear infection. You check for teeth. Nothing. The pediatrician shrugs. “Some babies are just fussy.”

But here’s the thing: this didn’t feel random. It felt like a switch flipped. Like your easy baby was replaced by a difficult one overnight.

What if it wasn’t random? What if there was actually a predictable pattern to these hellish phases? What if you could see them coming—and know they would end?

Frans X. Plooij and Hetty van de Rijt’s The Wonder Weeks claims exactly this. Their research identified ten predictable “leaps” in mental development during the first 20 months of life. Before each leap: fussy, clingy, crying baby. After: new skills, new understanding, new capabilities.

It’s been a lifeline for millions of exhausted parents. But is the science solid? And does knowing a leap is coming actually help? Let’s find out.


🎧 Want the Audiobook for FREE?

Before we dive in, here’s a little-known trick to get this audiobook at no cost:

  1. Click the link above to view The Wonder Weeks on Amazon
  2. Look for the “+ Audiobook” option when selecting your format
  3. Sign up for a free 30-day Audible trial
  4. Receive the full audiobook as part of your trial
  5. Keep the audiobook forever—even if you cancel the trial before it renews!

Listen while bouncing your fussy baby at 2am, cancel within 30 days, pay nothing, and keep the audiobook permanently. At least you’ll understand WHY they’re screaming. 🎧📚


What Is This Book? 🤔

The Wonder Weeks is based on decades of research by Dutch researchers Frans Plooij and the late Hetty van de Rijt. They observed infant development and identified patterns that seemed universal across cultures.

The core theory:
Baby brains develop in predictable spurts, not gradually. Before each developmental leap, babies become fussy, clingy, and difficult—their world is about to change, and that’s disorienting. After the leap, they emerge with new mental abilities.

The ten leaps:

  1. Leap 1 (Week 5): Changing sensations
  2. Leap 2 (Week 8): Patterns
  3. Leap 3 (Week 12): Smooth transitions
  4. Leap 4 (Week 19): Events
  5. Leap 5 (Week 26): Relationships
  6. Leap 6 (Week 37): Categories
  7. Leap 7 (Week 46): Sequences
  8. Leap 8 (Week 55): Programs
  9. Leap 9 (Week 64): Principles
  10. Leap 10 (Week 75): Systems

Each leap is preceded by a fussy period (the “stormy” phase) and followed by a “sunny” period where baby is happier and demonstrating new skills.

The book describes what’s happening in baby’s brain during each leap, what new abilities emerge, and how to support development during and after. 📖


The Good Stuff ✅

It Provides an Explanation When You Desperately Need One

The most valuable thing this book offers:

The experience without Wonder Weeks:
Baby is suddenly impossible. You don’t know why. You assume you’re doing something wrong. You worry something is wrong with baby. You feel helpless, confused, and increasingly desperate.

The experience with Wonder Weeks:
Baby is suddenly impossible. You check the chart. “Oh, we’re entering Leap 4. This is normal. This will end in about two weeks.”

The psychological relief:
Even if the fussiness is exactly the same, knowing there’s a reason—and an end date—changes everything.

The validation:
You’re not a bad parent. Your baby isn’t broken. This is a predictable phase of normal development.

The reframe:
That fussiness isn’t random misery. It’s your baby’s brain literally rewiring itself. The difficulty is the price of development.

Sometimes an explanation is all you need. 🎯

The “Three C’s” Framework Is Helpful

How to recognize a leap is beginning:

Clinginess:
Baby suddenly needs to be held constantly. Won’t be put down. Wants to be on you, with you, near you at all times.

Crankiness:
More crying. More fussing. Less easily soothed. Generally more difficult than usual.

Crying:
Increased crying that doesn’t seem connected to hunger, tiredness, or discomfort. Crying that can’t be explained or fixed.

Why this helps:
When you see all three C’s appearing together, you can suspect a leap rather than assuming something is wrong.

The pattern recognition:
After you’ve been through a few leaps, you start to recognize the pattern. “Oh, this feels like leap territory” becomes a useful shorthand.

Simple framework, practical application. ✨

It Helps You See Development in Real-Time

The book connects fussy phases to specific new abilities:

Leap 4 (Week 19) example:
Before: Extremely fussy, clingy baby who won’t nap.
After: Baby who can follow a toy as you move it, anticipate routines, notice cause and effect.

Leap 5 (Week 26) example:
Before: Separation anxiety suddenly appearing, nighttime waking, neediness.
After: Understanding that objects continue to exist when out of sight, recognizing spatial relationships.

Why this matters:
You start watching for the new skills. You notice development happening. You see the fussy phase as productive rather than just miserable.

The connection:
“The nightmare of the last two weeks produced THIS”—seeing your baby demonstrate new abilities gives meaning to the difficulty.

Fussiness becomes evidence of growth. 💪

The Predictability Reduces Parental Anxiety

Knowing what’s coming helps:

The calendar function:
The app (and book charts) let you see upcoming leaps. You can prepare mentally and practically.

The planning:
Don’t schedule a major trip during Week 19. Don’t start sleep training during a leap. Lower expectations during stormy phases.

The patience:
When you know a phase will end in 1-2 weeks, you can endure what feels unendurable.

The relationship protection:
“We’re in a leap” becomes shorthand between partners. It explains the chaos without blame. It sets realistic expectations.

The sanity:
Instead of “What’s wrong with my baby?” you have “We’re on day 6 of Leap 4. Five more days until sunny phase.”

Predictability enables endurance. 🌟

It Validates That Babies Are Working Hard

A helpful perspective shift:

The insight:
Baby isn’t giving you a hard time—they’re having a hard time. Their brain is undergoing massive changes. They’re overwhelmed by new perceptions they can’t yet process.

The analogy:
Imagine suddenly being able to see ultraviolet light, or hear frequencies you couldn’t before. Your world would be disorienting. You’d be overwhelmed. You’d want comfort.

The compassion:
Understanding that fussiness reflects genuine internal struggle helps you respond with empathy rather than frustration.

The message:
Your baby needs extra comfort during leaps not because they’re manipulating you, but because they’re genuinely overwhelmed.

The support:
Holding them more, responding more, being more present—this isn’t spoiling. It’s meeting a genuine developmental need.

Empathy through understanding. 🛡️

The Activity Suggestions Are Useful

Each leap chapter includes ways to support development:

Age-appropriate activities:
Games and interactions that align with emerging abilities. Things to try that match what baby is working on.

Environmental suggestions:
What to offer baby at each stage. How to set up their world to support new skills.

The practical value:
Instead of generic “play with your baby” advice, you get specific ideas matched to current developmental focus.

Examples:

  • During Leap 3: Games involving smooth movements
  • During Leap 5: Peek-a-boo and hiding games (object permanence)
  • During Leap 6: Sorting activities, categories, grouping

The engagement:
You’re not just surviving leaps—you’re actively supporting the development they represent.

Activities matched to development. 📝

The App Makes It Accessible

The Wonder Weeks app extends the book’s usefulness:

What the app offers:

  • Personalized leap calendar based on due date
  • Push notifications when leaps begin
  • Tracking of fussy periods
  • Shorter, accessible content

The accessibility:
No one has time to read during the newborn phase. The app puts the information where you need it—on your phone at 3am.

The community:
Knowing millions of other parents are going through the same thing at the same time provides solidarity.

The modern format:
For parents who won’t read a whole book, the app delivers the core value in digestible format.

Meeting parents where they are. 📱


The Not-So-Good Stuff 😬

The Science Has Been Seriously Questioned

This is the big one:

The controversy:
In recent years, researchers have challenged the scientific validity of the Wonder Weeks model. Studies attempting to replicate the findings have failed to confirm the predictable patterns.

The critiques:

  • Original research methodology questioned
  • Fussy periods don’t align with leaps as precisely as claimed
  • Developmental milestones vary more widely than the model suggests
  • The “leaps” may be confirmation bias—we notice what we’re looking for

The 2019 study:
A large-scale study found no evidence for the predictable fussy periods the Wonder Weeks model claims. Babies were fussy at all sorts of times, not clustered around specific weeks.

The honest assessment:
The Wonder Weeks model may be more helpful as a framework for understanding that development happens in spurts than as a precise predictive tool.

The implication:
The specific week numbers may be less reliable than the book claims. Your baby may not follow the pattern.

Popular doesn’t mean proven. 😬

It Can Create Anxiety Instead of Relieving It

The shadow side of predictability:

The worry:
“We should be in the sunny phase by now. Why is my baby still fussy? Is something wrong?”

The comparison:
“Other babies are showing these skills after Leap 4. Mine isn’t. Is my baby delayed?”

The hypervigilance:
Constantly checking the app. Attributing every fuss to a leap. Over-interpreting normal baby behavior.

The trap:
The tool meant to reduce anxiety can increase it if you hold it too tightly.

The truth:
Babies don’t read the book. They develop at their own pace. The Wonder Weeks provides a general framework, not a precise roadmap.

The balance needed:
Use it loosely. Don’t panic if your baby doesn’t match the pattern.

Framework, not prescription. 🚩

The Timing Isn’t Reliable for Many Babies

Individual variation is real:

The claim:
Leaps happen at predictable weeks, calculated from due date.

The reality:
Many parents report their babies don’t align with the predicted weeks. Some are early, some late, some seem to skip leaps entirely.

The problem:
If you’re watching for Week 19’s leap and it comes at Week 16 or Week 22, the predictive value diminishes.

The variables:
Premature babies, developmental differences, individual variation—the one-size-fits-all timeline doesn’t fit all.

The frustration:
“This doesn’t work for my baby” is a common complaint.

The adjustment:
Treat the weeks as approximate. Look for the three C’s rather than the calendar.

Your baby’s timeline is their own. 📉

Confirmation Bias Is Real

We see what we’re looking for:

The pattern:
You read about Leap 4. You watch for Leap 4. Baby has a rough day—”It’s Leap 4!” Baby has a good day—”We’re in the sunny phase!”

The problem:
Babies have fussy days regardless of leaps. If you’re expecting fussiness, you’ll attribute any fussiness to the leap.

The research concern:
This is exactly what critics argue—the Wonder Weeks pattern may exist primarily in how parents interpret normal variation.

The reality check:
Would you notice the same “leap” if you weren’t watching for it? Maybe not.

The question:
Is the pattern real, or do we create it by believing in it?

The value either way:
Even if it’s partly confirmation bias, having a framework that helps you expect and endure difficulty isn’t worthless. But it’s worth knowing the limitation.

Helpful fiction is still fiction. 🧠

It Doesn’t Account for All Fussiness Causes

Leaps aren’t the only explanation:

Other reasons babies are fussy:

  • Teething
  • Illness
  • Sleep debt
  • Hunger
  • Growth spurts (separate from mental leaps)
  • Overstimulation
  • Understimulation
  • Temperature
  • Digestive issues
  • Just having a bad day

The risk:
Attributing everything to “a leap” and missing actual issues that need attention.

The danger:
“Oh, they’re just in a leap” when actually they have an ear infection.

The balance:
Wonder Weeks can be ONE explanation. It shouldn’t be the only one you consider.

The check:
Rule out physical causes before assuming developmental explanation.

One tool, not the whole toolkit. 🩺

The Writing Is Repetitive and Padded

A familiar complaint:

The pattern:
Each leap chapter follows similar format with similar descriptions. The core content could be condensed significantly.

The experience:
By Leap 5, you’re skimming because you’ve read the same structural content four times already.

The padding:
Parent testimonials, extensive repetition of concepts, examples that blur together.

The solution:
Many parents prefer the app precisely because it distills the content. The book itself can feel like more than necessary.

The reality:
You don’t need to read every word. Skim for the leap-specific content, skip the repetition.

Core content buried in padding. 😬

It Ends at 20 Months

The coverage has limits:

What’s covered:
Birth through approximately 20 months (75 weeks).

What’s not covered:
Toddler development after 20 months. All the fussiness and leaps that continue beyond.

The cliff:
You’ve become dependent on the leap framework, and suddenly it ends. What now?

The gap:
Development doesn’t stop at 20 months. But Wonder Weeks does.

The resources needed:
Other books for toddler development and beyond.

Helpful window, then you’re on your own. 📉

Neurodivergent Development May Not Fit

The familiar blind spot:

The assumptions:
Neurotypical development following typical patterns.

What’s not addressed:

  • Babies who will later be identified as autistic
  • Developmental delays
  • Premature babies with different trajectories
  • Babies with sensory processing differences

The problem:
When your baby doesn’t fit the pattern, the framework offers no guidance—just the sense that something might be “wrong.”

The gap:
No discussion of when developmental differences might indicate something other than normal variation.

The adaptation needed:
Parents of babies with different developmental trajectories may find the Wonder Weeks framework unhelpful or even anxiety-producing.

Typical development assumed. 🧠

The Due Date Calculation Is Problematic

The timing foundation is shaky:

The method:
Leaps are calculated from due date, not birth date—to account for babies born early or late.

The problem:
Due dates are estimates. They can be off by weeks. Calculating leaps from an imprecise date creates imprecise predictions.

The compounding error:
If your due date was wrong, your leap predictions will be off throughout.

The variability:
Even accurately-dated babies don’t develop on the same schedule.

The reality:
The precision implied by “Week 19” is false precision. Development isn’t that predictable.

Precise numbers, imprecise reality. 😬


Who Is This For? 🎯

Perfect if you:

  • Have a baby under 20 months
  • Want a framework for understanding fussy periods
  • Find comfort in predictability and explanation
  • Can hold the information loosely without becoming anxious
  • Need validation that fussiness is normal and temporary
  • Want activity suggestions matched to developmental stages
  • Appreciate having something to blame at 3am

Not ideal if you:

  • Tend toward anxiety and might obsess over the predictions
  • Have a baby who doesn’t fit typical developmental patterns
  • Want heavily evidence-based, scientifically validated information
  • Need your baby to follow the timeline for your own sanity
  • Are looking for solutions to fussiness (this explains, doesn’t fix)
  • Have a baby older than 20 months

Alternatives Worth Considering 🔄

The Montessori Baby by Simone Davies: Different framework for understanding infant development. Less focused on fussy periods, more on supporting development through environment. Complementary approach. 🏆

Precious Little Sleep by Alexis Dubief: If sleep disruption is your main concern, this addresses it more directly than Wonder Weeks’ developmental framework.

The Happiest Baby on the Block by Harvey Karp: For the newborn period specifically. Practical soothing techniques rather than developmental framework.

Cribsheet by Emily Oster: Data-driven approach to infant decisions. More scientifically rigorous framework for understanding baby development.

The Whole-Brain Child by Daniel Siegel & Tina Payne Bryson: Brain science approach to child development. Continues beyond where Wonder Weeks ends, with stronger scientific foundation. 📚


The Final Verdict 🏅

The Wonder Weeks has helped millions of parents survive the bewildering first year and a half of their baby’s life. The framework—that development happens in predictable spurts preceded by fussy periods—provides explanation, validation, and hope. The three C’s give you something to look for. The leap descriptions help you understand what’s happening inside that little head. And the predictability, even if imperfect, offers comfort when you’re drowning.

For exhausted parents who need to believe this phase will end, the book delivers.

However, the science has been seriously questioned. The predictive precision the book claims may not hold up. Individual variation is enormous. And the framework can create anxiety as easily as it relieves it if you hold it too tightly.

The useful parts:

  • Framework for understanding developmental spurts
  • Validation that fussiness is normal and temporary
  • The three C’s as recognition tool
  • Activity suggestions matched to developmental stages
  • Predictability (however imperfect) enables planning
  • Perspective shift: fussiness as development, not defect
  • App accessibility for sleep-deprived parents

The problematic parts:

  • Scientific validity seriously questioned
  • Can increase anxiety if held too rigidly
  • Timing unreliable for many babies
  • Confirmation bias may create the pattern we see
  • Doesn’t account for other fussiness causes
  • Repetitive, padded writing
  • Ends at 20 months
  • Neurodivergent development not addressed

The best approach: Use the Wonder Weeks as a loose framework, not a precise prediction. When your baby is having a tough phase, check if it aligns with a leap—but don’t panic if it doesn’t. Use it for comfort and general understanding rather than exact expectations.

The bottom line: The Wonder Weeks is best understood as a helpful story rather than settled science. The story—that your baby’s fussiness serves a purpose, that difficulty precedes growth, that this phase will end and leave new capabilities in its wake—is a useful story. It helps you endure. It helps you respond with compassion. It helps you see your struggling baby as a developing human rather than a problem to solve.

Whether the specific weeks and leaps are precisely accurate matters less than whether the framework helps you get through.

And for millions of parents, it has.

At 3am, when your baby is screaming and you’re crying and nothing makes sense, sometimes you just need someone to say: “This is normal. This is temporary. This means something. You’re both going to be okay.”

The Wonder Weeks says that. Whether or not it’s scientifically perfect, it might be exactly what you need to hear. 👶✨


Did the Wonder Weeks help you understand your baby’s fussy phases? Did your baby follow the predicted leaps? What was your experience with the framework? Share your thoughts below!

Comments

Leave a Reply

Your email address will not be published. Required fields are marked *