mfe
Li enn letid longitidinal lor enn period 8 an, ant 1983 a 1991. Sa letid-la konsern 51 lekol primer dan distrik California, Texas, Florid, New York ek New Jersey.
eng
He did an eight-year longitudinal study, 1983 to 1991 in 51 different primary schools in the States of California, Texas, Florida, New York and New Jersey.