Is there any evidence for the wonder weeks?

What the evidence says

The Wonder Weeks is a popular book and app that says babies go through 10 fussy periods at very specific, predictable weeks, each followed by a mental "leap." It sounds neat and tidy, but the science behind those exact numbers is thin.

The theory was created by a Dutch researcher couple who watched a small number of babies at home and wrote down when fussiness seemed to happen. Later, the same authors published their own study checking whether their program helped parents. That is not the same as independent scientists, pediatric groups, or big Canadian or American health bodies testing and confirming the theory.

What we do know, from real research, is that babies genuinely do go through growth spurts and fussy stretches in the first two years. Growth in babies happens in bursts rather than a smooth line, and crying, wanting to feed more, and general fussiness are common and normal during these times.

However, research also shows these fussy periods do not fit into one tidy schedule that works for every baby. A review looking at many studies found that fussiness, crying, and feeding changes get blamed on things like low milk supply or growth spurts more often than the evidence actually supports, because babies vary a lot and these behaviors are hard to time precisely.

So the bottom line for a parent: your baby probably will have fussy weeks and calmer weeks, and that is completely normal. But you don't need to worry if your baby's fussy times don't match the exact weeks the book lists. There's no solid science saying every baby follows that specific calendar.