Developmental Psychology & Attachment

Developmental psychology studies how people change — cognitively, emotionally, socially — from infancy onward. Two of its most famous real contributions sit at very different points on the "how well does this hold up" spectrum this course keeps returning to: one is a genuinely durable, well-replicated framework; the other is a beloved popular story whose real predictive power turned out to be substantially smaller than its own legend.

Bowlby & Ainsworth: Attachment Theory

John Bowlby, a British psychiatrist, developed the real foundations of attachment theory across the 20th century, publishing his defining trilogy Attachment and Loss between 1969 and 1982. His real, central claim was that infants have a biologically built-in need to form a close bond with at least one primary caregiver — drawing on evolutionary biology and ethology as much as clinical observation — and that a caregiver's real sensitivity and responsiveness between roughly six months and two years of age shapes whether that bond becomes secure.

Mary Ainsworth turned Bowlby's theory into something testable. Her real Strange Situation procedure, developed across the 1960s and 70s, was a 21-minute structured laboratory observation involving seven episodes in which a mother, an infant, and a stranger moved in and out of an unfamiliar room containing toys — watching precisely how the infant reacted to separation from, and reunion with, the caregiver.

Mischel's Marshmallow Test: A Beloved Story, a Much Smaller Real Effect

Walter Mischel's famous delayed-gratification study is one of psychology's most widely retold results. The real, iconic version was run in 1972 (Mischel, Ebbesen, and Zeiss) with just 50 children — 25 boys and 25 girls — from Stanford University's own Bing Nursery School. Each child was left alone with a marshmallow (or similar treat) and given a real choice: eat it right away, or wait roughly 15 minutes for the researcher to return and receive a second one as a reward.

Follow-up studies conducted years later reported that children who waited longer as preschoolers went on to show real, statistically measured advantages — "significantly more competent" adolescent behavior in a real 1988 follow-up, and higher real SAT scores in a 1990 follow-up, plus later associations with better educational attainment and lower adult BMI. This is the version of the story that made it into countless parenting books and TED talks: that a four-year-old's willpower alone predicts their whole future.

In other words, a real, substantial share of what looked like "waiting longer as a preschooler predicts later success" was actually standing in for something else entirely: children from more stable, resourced homes tend to both wait longer for a marshmallow and go on to do better later — not necessarily because the waiting itself caused the later success, but because both outcomes shared a real, common upstream cause in family circumstances.

Why the Comparison Matters

This isn't a reason to distrust developmental psychology generally — it's the same lesson Chapter 6 delivered about Zimbardo's prison study, applied to a completely different, gentler-sounding finding: a small, homogeneous original sample can produce a real result that simply doesn't generalize once tested on a real, more representative population.

Hands-On Exercises