Jean Piaget 1896 – 1980 Stage theory of cognitive development Four stages -highly influential -the mind unfolds with age -emphasis on normal child
Critique: Little concern with environmental effects Observations of his own children Underestimated abilities
Learning theories It’s all conditioning Gradual accumulation of S-R links No systematic stages Allows for differences
The arrangement of siblings: Family Constellation Effects e.g. birth order, family size, etc.
examples FAMILY AFAMILY BFAMILY C Charles17Alec 9Pierre 15 Anne15Daniel 7 Andrew 5Bill 4 Edward 1Stephen 1
Includes grades, IQ, SAT, etc. Zajonc (1979) collected large datasets on families Noticed effects of arrangement of children: eg birth order, family size, spacing, etc. Intellectual Achievement (IA)
Six facts to be explained: 1. IA declines with birth order 2. IA declines with greater family size. 3. IA declines with close-spacing 4. IA declines with multiple births 5. IA declines with only children 6. Last-borns show extra decline
Confluence Model: Two propositions Proposition I. Mental stimulation of the child leads to permanent improvement in ability Explains facts 1-4
Zajonc says do the math: - Estimate degree of mental stimulation by average level of mental age in family Childless couple: MS = (16+16)/2 = 16 At birth of first-born: MS = (16+16+0)/3 = 10.67 At birth of second born: MS = (16+16+2+0)/4 = 8.5
How to explain facts 5 & 6 ? Proposition II: The Teaching Effect Last-borns don ’ t get to teach Teaching aids the teacher Consistent with research on memory, peer-tutoring, etc.
Followup study by Paulhus and Shaffer data on 20, 000 students SAT scores Number of younger siblings Number of older siblings gender
Results Boys more older sibs reduces SAT more younger sibs reduces SAT Girls more older sibs reduces SAT More younger sibs increases SAT
Interpretation Teaching effect is more than all-or-none But only works for girls Sex roles must have an impact
Kristensen & Bjerkedal (2007) All Norwegian males have their IQ tested by the military N = 250, 000 First borns > second borns Confirmed effect of birth order Actually effect of raising order
Summary Confluence Model is parsimonious Explains 6 facts with two propositions Entirely environmental Effects are small -- but interesting