The Role of the Family in the
Development of Mental
Abilities: A 50-year Study1
Marjorie P. Honzik
Institute of Human Development
University of California, Berkeley
For over half a century I have been interested in the mental development of infants, children and, in more recent years, adults. My research has been largely has been largely analyzing the mental test records of individuals who were tested repeatedly over long periods of time. This chapter presents an overview of what we now know about individual differences in mental growth, based on longitudinal research at the Institute of Human Development at the University of California at Berkeley; at other centers in the United States, such as Fels; and at five research centers in Europe coordinated by the International Children's Center in Paris ( Falkner, 1955). The five European longitudinal studies are situated in London, Stockholm, Brussels, Paris and Zurich. These investigations all began in 1955, when the children to be followed were born. The children's physical, mental, and behavioral development was assessed until age 17.
Fifty years ago, when the Berkeley and Fels studies were initiated, we thought we knew a great deal about the development of intelligence. Terman ( 1919) and others had provided excellent tests that were reliable, and he reported that the test scores were highly predictive over the age periods studied (the average correlation was .93). In other words, he stated that on the basis of the evidence, the IQ is constant. However, an early finding in the field of mental testing was that although the trend is for individuals to maintain their relative positions in the group over time, there are always instances of changes, even marked changes, in scores. These changes do not appear to be____________________