Wonder Weeks: Understanding the Theory and the 10 Leaps

Per a popular parenting manual, babies go through phases of both contentment and fussiness. This behavioral fluctuation is considered a positive indication of major developmental strides known as the “Wonder Weeks.”

“Wonder Weeks” is a term coined by Dutch parenting authors Dr. Frans X. Plooij and Hetty Van de Rijt to describe the intense periods of development in an infant’s life. Peak changes within these Wonder Weeks are called “leaps” with each one likened to a mental growth spurt as new skills are developed.

To come to grips with the Wonder Weeks hypothesis, we’ll break each of the 10 leaps down in detail, take a look at the science behind it, evaluate its accuracy, explore the controversy surrounding the theory, and more.

What Is the Wonder Weeks Theory?

Co-authors of the 1992 book The Wonder Weeks suggested that “sudden age-linked brain changes are a direct causation of the fussy behaviors babies present during age-linked recession periods.”

These developmental changes are described as “mental leaps,” and the book coined the term “Wonder Weeks” to describe how specific weeks of a baby’s life correspond to these developmental “leaps.”

The book (get your copy here) argues that during this timeline of leaps, your baby will have a “sunny week” exhibiting good behavior and a generally stable temperament followed by a “stormy week” (which can last between 1-4 weeks).

In the wake of this rough patch, the co-authors suggest, a “Wonder Week” will then emerge in which your child supposedly hits a developmental milestone.

The authors proposed that by outlining these challenges and changes into a schedule of “leaps,” parents would be able to anticipate them and help their child feel less frustrated as they make each of these difficult transitions.

Wonder Weeks Author

The Wonder Weeks is the English translation of the Dutch book Oei, ik groei! (Ai, I’m Growing!) originally published in 1992 by husband-and-wife team Dr. Frans X. Plooij and Hetty Van de Rijt.

With their collective backgrounds in behavioral science, educational psychology, and physical anthropology, the pair developed the Wonder Weeks concept in the early 1980s.

The Wonder Weeks remains a bestseller and has been translated into over 20 languages. There is even an award-winning mobile app based on the book.

Is There Any Science Behind Wonder Weeks?

As every child develops in their own time, the authors’ assertion that all babies experience predictable, age-linked changes has been greeted with skepticism by many parents.

However, the authors’ many years of observation of infant development make a compelling case for the theory.

Throughout their research, similar regression periods were observed in baby chimpanzees in Tanzania and human infants in the Netherlands.

Dr. Plooij has also discussed the relatively new scientific discipline of psychoneuroimmunology, which explains that each bodily system interlinks and influences the others.

Therefore, an imbalance seen in just one system (such as illness due to a weakened immune system) must be identifiable in multiple systems, linking them to a general developmental change.

Is Wonder Weeks Reliable?

For some parents, Wonder Weeks has been described as accurate and sanity-saving with moms sharing that it has helped them to “find the grace and patience to roll with whatever my child needs to make him/her feel safe and secure in an overwhelming time.”

Experts have also praised the book for clarifying aspects of the parent-child connection with Oxford Head of Pediatric Psychology John Richer noting:

“The authors describe these stages in the infant’s understanding, outlining the play and communication that works best with babies at different ages, thus helping parents connect sensitively with their babies.”

That being said, some parents put the theory’s success down to confirmation bias (the idea that a one-off validation of a leap happening will make the connection in our mind that this is a real and accurate science).

Mom blogger Ashley Olsen from Heaven Sent Sleep has likened Wonder Weeks to “baby horoscopes.”

What Weeks Are the Wonder Weeks?

The Wonder Weeks occur within the first two years of a child’s life, beginning from five weeks up to around 20 months of age. The leaps and corresponding weeks are as follows:

  • Leap 1 – from week 4/5
  • Leap 2 – from 7 weeks
  • Leap 3 – from 11 weeks
  • Leap 4 – from 14 weeks
  • Leap 5 – from 22 weeks
  • Leap 6 – from 33 weeks
  • Leap 7 – from 41 weeks
  • Leap 8 – from 50 weeks
  • Leap 9 – from 59 weeks
  • Leap 10 – from 70 weeks

Do Wonder Weeks Go by Due Date or Birthdate?

According to The Wonder Weeks site FAQs, the weeks go by your due date based on the 40-week gestation period (preemie and twin babies are included in this calculation).

The Wonder Weeks go according to the due date because “the brain’s development begins at conception, and by using the due date, we can tell when your baby will make a leap with a margin of two weeks either side.”

How Long Does a Wonder Week Last?

A Wonder Week can last “anywhere from a few days to a few weeks (sometimes six weeks), and the length can increase as the child gets older” according to Mom blogger Rachel Rowell of My Baby Sleep Guide.

Officially, The Wonder Weeks website suggests that the duration of each Wonder Week depends on your child’s interests and that some skills will overlap from leap to leap, so it’s “not important to know how long a leap lasts.”

Can a Wonder Week Start Early?

Yes, depending on your due date and your baby’s actual birth date “the initial leap can come a little sooner or later,” according to Wonder Weeks author Dr. Plooij, so any subsequent leap could feasibly start earlier than stated.

Wonder Weeks Leaps

Within each of these major “leaps,” your child will undergo dramatic changes, beginning each leap with a fussy phase of more crying and crankiness than usual.

While this seems like regression, Plooij and Van de Rijt point out that this signals that a positive learning opportunity is on the horizon.

Wonder Weeks Leap 1

Dubbed “the world of sensations,” the first leap sees your baby become increasingly sensitive to new experiences and stimuli.

They’ll enter a fussy phase of being crankier and clingier than usual before beginning to adjust to new sensations (around week 6) with greater curiosity about their world.

Stimulate their senses in this phase by introducing them to colors, contrasts, and new faces.

Wonder Weeks Leap 2

No longer viewing their world as one big mess of stimuli, your baby begins to see and discover fixed “patterns.” Automatic reflexes will be replaced by a conscious “feeling” of their body and the things their body can do.

They’ll still exhibit the three C’s of Leap 1 (crying, crankiness, and clinginess) and will crave more variation in their day.

Wonder Weeks Leap 3

Your baby will acquire the skill of seeing the world in smoother transitions (for example, the brightness of lights changing, objects moving, etc.) and begin to handle the complexity of these things a little better and enjoy them as part of play!

They may also appear shyer, suck their thumb, and have a loss of appetite. Movements may appear less wooden and jerky during this time too, and this is quite evident from the way they play with the sound of their voice.

Wonder Weeks Leap 4

Sensations and patterns that didn’t quite feel connected together are now beginning to form one big event in your baby’s understanding of the world.

Practicing their new-found skills and perspectives after this leap, the baby may show more sophisticated language and motor skills, such as grabbing objects, babbling, and enjoying children’s songs and nursery rhymes.

Wonder Weeks Leap 5

This is considered a giant developmental leap and is known as the “relationship phase.” Around this time, your child begins to understand that all their previous leaps are like puzzle pieces that now fall into place.

In exploring his/her understanding of relationships of things to one another, for example, they can perceive how a toy block can be placed on top, behind, or underneath another block.

Place an empty basket and their toys beside the basket next to them to encourage them to place things in/out/around an object.

A six-month-old baby lying on her tummy while playing with toys.

Wonder Weeks Leap 6

Your child can now begin dividing their world into recognizable groups and categories. They understand, for instance, that certain things have the same look, smell, sound, or taste as others.

Encourage them to play with different weighted/sized objects to help them play with the concept of big and small, low and high, etc.

Extreme change at this stage also brings resistance — they become more restless during diaper changes and much fussier when it comes to eating.

Wonder Weeks Leap 7

In a fit of clinginess, your child will not like to break body contact with you, appearing more reserved and craving to be entertained and attended to by you and you alone.

In an amazing skill development though, your child is able to identify and name different things, animals, and people (admittedly with babble and not actual words), but the recognition is beginning to form!

Wonder Weeks Leap 8

They are now transitioning from baby to toddler and appear less helpless.

Remarkably, they also begin to piece sequences of action into one whole process (e.g., picking up a dirty dish, scrubbing it with a brush, and placing it on the rack is recognized as “washing the dishes”).

On the flip side, this leap can see them regress to shyer, clingier behaviors of past leaps in addition to jealous behaviors and poorer sleep.

Wonder Weeks Leap 9

A huge mental and psychological milestone, your toddler can now imitate others, demonstrate an understanding of thinking ahead, and reflect on and consider the consequences of their actions.

With this big change also comes a lot of irritability and frustration from your little one, particularly if you are not immediately available to them or when something doesn’t go their way.

Wonder Weeks Leap 10

In exploring their world for over a year now and approaching their second year on this planet, your toddler is beginning to apply the skills they have learned both in and outside their home.

Tantrums and poor sleep are still a thing, but a wonderful trade-off is their willingness to do more things for themselves, including play, entertainment, and activities.

They can also recognize that others may not share their preferences, and they recognize themselves as individuals (boy are they individuals by now!).

Wonder Weeks Chart

Wonder Weeks Leap(Approx.) AgeBehaviorsSkills/Developments
Leap 11 monthSensitive, curiousCuriosity and exploration of new sensations, colors, faces
Leap 22 monthsClinginess, crankiness, needing variationConsciously feeling with their hands, discovering patterns
Leap 32.75 monthsShyness, thumb-sucking, appetite lossViewing world in smoother transitions
Leap 44.5 monthsBabbling, grabbing objects
Connecting patterns, enjoying songs
Leap 56 monthsPlaying with greater curiosity and complexityPiecing previous leaps into place, understanding relationship of objects
Leap 68.5 monthsFussy eating, restless during diaper changesDividing world into categories (familiar smells/tastes/sounds, etc)
Leap 710.5 monthsBabbling, shyness, clinginessRecognizing and identifying different things/people
Leap 81 year and .75 months (50-55 weeks)Jealousy, poor sleep, clinginessCan piece “sequences” into one concept
Leap 91 year and 2.5 months (59-64 weeksIrritability, frustrationAbility to imitate, think ahead, and reflect on actions
Leap 101 year and 6 months (70-80 weeks)Poor/disturbed sleep, tantrumsRecognition of self, love of independent play/activities

What Is the Hardest Wonder Week?

Parents have observed that any leap associated with a drastic change in sleep patterns and greater clinginess was found to be the most difficult.

For some, this can appear in Leap 4 or Leap 10, but it may appear at different times depending on your baby’s personality.

Wonder Weeks App

A popular Wonder Weeks app has been developed, guiding you through the signals of each leap and the skills your child can expect to acquire.

It allows you to keep a personalized chart of the child’s leaps and includes many unique games to encourage their skill development.

Wonder Weeks Controversy

A research assistant of Dr. Plooij attempted to replicate the study of the concept of “Wonder Week leaps,” but he was unable to do so.

Findings published by Ph.D. student Carolina de Weerth concluded that “age-related regression periods do not exist, and infant development is chaotic with wide variation.”

This has led to claims that Plooij may have falsified his research.

Beyond the Wonder Weeks

Beyond Leap 10, your child will continue to have fussy periods and sleep regression as their skills develop at a rapid pace.

Psychologist and parenting author Vanessa Lapointe explains that throughout childhood, kids will have moments of disturbed sleep, clumsiness, and a short fuse:

“This is because of a hyper over-development of neural connections, and this will be at its most prolific for the first six to 8 years of life.”

Closing Thoughts

Essentially, the “Wonder Weeks” describe the significant developmental milestones your child goes through in their first 2 years, categorized into 10 leaps.

Many parents have found that the Wonder Weeks book has given them great insight into their child’s development.

It’s important to take this (or any book) with a grain of salt, however, remembering that each child will develop skills and behaviors at different rates.

After all, viewing these leaps as gospel could cause anxiety when they don’t occur in the time frame outlined by the authors.