The report, by Larry V. Hedges and Amy Nowell of the University of Chicago, analyzed six large national surveys of American male and female teen-agers’ performance on tests of mental ability conducted over the past three decades.

The study, published in Friday’s issue of the journal Science, found that the average sex differences in most measured abilities were small. Nevertheless, the differences in performance seen in science, mathematics, reading and writingcombined with the fact that boys’ scores tended to vary more widely than girls’ frequently produced situations where boys greatly outnumbered girls at the top or bottom of the scale.

For example, seven times as many boys as girls scored in the top 5 percent on science tests, and about twice as many boys as girls scored

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see TEST, page 6