Abstract
Based on the authors' parallel longitudinal studies from birth to maturity, we describe and discuss a series of practical and theoretical matters. In the matter of design, we review criteria for deciding the degree of compatibility in time series of test results. Concerning measurement, we review attrition, testing and international conventions for presenting data. The concept of social class within SES data is addressed. The effect of the passage of real time on tests is considered and illustrated from our two testing schedules. Tests are also addressed in relation to differing cultural settings and the availability of culture-fair tests.