American technical and economic preeminence are reported to be at risk from students' diminished intellectual ability, demonstrated until recently by declining precollege test scores. But aptitude gains are also reported. Average intelligence quotient rose substantially for persons born between 1900 and 1967, although IQ declined for those born in the depression and postwar baby boom. Time-series regression shows that 80% of the variation in cohort IQ over time can be explained by variation in early childhood nutrition and family size. Improving the environment of the first years of life seems a key to increasing the intellectual capability and productivity of Americans. (Author)