This report examines 1974-1975 achievement test results for Philadelphia Follow Through pupils in the light of "quasi-longitudinal" variables from the Follow Through longitudinal pupil file. In Part I, Head Start effects are examined by comparing the Head Start group and the Non Head Start group of pupils within the maximum exposure category at each grade level. Evidence is presented for three effects: the effect of Head Start or equivalent preschool experience, the effect of maximum program exposure, and the effect of low absence. These effects were found to show a good degree of consistency for the Total Follow Through population. Model-specific variation is discussed. In Part II, the actual levels of performance were examined for four quasi-longitudinal groupings: the total group tested (cross-sectional), pupils with maximum program exposure, pupils with maximum program exposure and Head Start or equivalent experience, and pupils with maximum exposure, Head Start or equivalent experience and fifteen or fewer days of absence. The general pattern of results indicates increasingly higher levels of performance with each increasingly restrictive grouping as expected. Model-specific variation is noted for three time-points: first program grade (kindergarten), final program grade (third), and highest grade of program "graduates" (sixth). The importance of strictly longitudinal analysis for better emphasis of these effects vis-a-vis other variables is emphasized. (JMB)