The Wonder Weeks: A Stress-Free Guide to Your Baby's Behavior is a book with advice to parents about child development by physical anthropologist Hetty van de Rijt and ethologist and developmental psychologist Frans Plooij. Their daughter Xaviera Plas-Plooij is a third author of recent editions. It was first published in English in 2003 as the translation of the 1992 Dutch book Oei, ik groei! The book claims that the cognitive development of babies occurs in predictably timed stages. Ever since the systematic study of child development began at the beginning of the 20th century researchers have disagreed whether this is gradual or in punctuated stages. Some figures in the child development field have objected that sleep regressions are not so predictable. A chapter on sleep was added to the 6th edition in 2019. The publisher has produced a mobile app based on the book.
Claims The book describes 10 predictable 'leaps' observed in a child's cognitive development during the first 20 months, with 8 in the first year. (Months are counted from the due date because development begins with conception.) They are predicted to occur at about 5, 8, 12, 17, 26, 36, 44, 53, 61-62 and 72-73 weeks old. Each developmental 'leap' is said to begin with a regression period in which the baby becomes more insecure, clinging, and cranky, followed by a longer period in which the baby is more happy gaining confidence with new perceptions and skills. The book claims that this enables parents and caregivers to make better choices of age-appropriate toys, activities, and interactions to support the baby's development at each stage.
Scientific basis Ethologists have documented predictable 'regression periods' in the interactions of mothers and infants in many species, suggesting an early origin in evolution. In the course of a 1971-1973 longitudinal ethological study of chimpanzees in the wild, working with Jane Goodall, van de Rijt and Plooij published additional data demonstrating predictable regression periods in Chimpanzee mother-infant dyads, the correlation of illnesses with these, and the importance of the mother's interactions for the baby's growing independence and learning. They hypothesized a new type of learning important in the evolution of human parenting, with reference to an explanation in control theory. To test this hypothesis, they applied the observational methodology of ethology to human mothers and infants. Their first human study, involving 15 Dutch mothers and their infants, with extrinsic sources of stress carefully controlled, was published in the Journal of Reproductive and Infant Psychology in 1992. Independent replication studies were carried out at universities in four culturally divergent countries. Three were presented in a symposium held at Göteborg University Sweden on October 10—11, 1997 (The First Research Conference on Regression Periods in Early Infancy) and published in 2003: Groningen in the Netherlands, Oxford in England, Gothenburg in Sweden, and Girona in Spain. The Spanish study was also published in a peer-reviewed journal. Another peer-reviewed study included verification of parents' reports that babies master a cluster of new skills after each regression period. Research by Colwyn Trevarthen and Kenneth J. Aitken into development of the central nervous system has identified periods of rapid change (PRC) which coincide with the observed regression periods, and known stages of neurological development of the brain have been correlated with the behavioral observations. Consistent with the hypothesis of increased stress, a correlation between regression periods and upticks of illness has been reported, and a correlation with SIDS. A 2020 newspaper article about 'sleep regressions' quotes some professional skepticism and caution. Dr. Jodi Mindell, Ph.D., a child psychologist specializing in sleep at Children’s Hospital of Philadelphia, has objected that for a theory of sleep patterns “it has to be a very large sample. I think that means looking at thousands of babies.” Dr. Kathy Hirsh-Pasek, Ph.D., a psychologist who studies infant language at Temple University in Philadelphia, said that she had “never heard of anything that is that prescriptive”, but “we really are at the infancy of infant brain knowledge”. However, Dr. Pamela Hops, M.D., a pediatrician in New York City, said “I think he’s spot on, shockingly so” and that during her 20 years of practice, she has anecdotally seen and heard about changes in babies that perfectly align with the 10 leaps Dr. Plooij described.
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