Erikson, Piaget & Psychology Theories & Concepts Explained

Social Identity Theory: What Tajfel & Turner Said in 1979

Social identity theory, developed by Henri Tajfel and John Turner in 1979, proposes that part of who you are comes from the groups you belong to, and that people favor their own groups to protect a positive sense of self. That sounds obvious until you see the evidence behind it. In the early 1970s, teenage boys sorted into groups by...

Vygotsky’s Sociocultural Theory: ZPD, Scaffolding, Play & How Culture Shapes Learning

Vygotsky’s sociocultural theory, often called Vygotsky’s theory of cognitive development, proposes that learning is fundamentally social. Children build knowledge through interaction with others, guided by more skilled partners and the tools their culture provides. Its best-known ideas are the zone of proximal development, scaffolding, and the role of language in thought. But a few things students “know” about this theory...

Ecological Theory of Aging: Bronfenbrenner vs Lawton Explained

The ecological theory of aging holds that how well someone ages depends on the fit between that person and their surroundings, not on health or age alone. Picture two 80-year-old women who break a hip in the same week. Six weeks later, one is back at her Thursday book club. The other hasn’t left her apartment since the hospital sent...

Between Subjects vs Within Subjects: Why People Rated 9 Bigger Than 221

Imagine asking one group of people how big the number 9 is, and a different group how big 221 is. In a real study, the group judging 9 gave it the higher rating (Birnbaum, 1999). Nobody forgot how numbers work. The result came from the experimental design. The choice between subjects vs within subjects decides whether each participant experiences one...

Bronfenbrenner’s Ecological Systems Theory: How Your Environment Shapes Who You Are

Bronfenbrenner’s ecological systems theory proposes that human development is shaped not by a single factor, but by five layers of interconnected environments – from your immediate family and classroom all the way to the broader culture you live in. Developed by Urie Bronfenbrenner in the 1970s, this framework is a cornerstone of developmental psychology and a core topic in AP...

Replication Crisis in Psychology: Which Famous Studies Failed?

Imagine citing a famous study in your term paper, then finding out that 23 labs tried to reproduce it and came up with almost nothing. That is the everyday reality of the replication crisis in psychology. Since the early 2010s, researchers have been re-running the field’s best-known experiments, and the results have been humbling. Some celebrated findings collapsed. Others survived...