Sweat clothes will be the school uniform for boys and girls some days; but at other times the same students will show their cool in clothes that grown-ups enjoy: tuxedo shirts, walking shorts, banker's gray pin stripes, suspenders, big collars, blousons, and camel's-hair blazers. Scaled-down versions of grown-up favorites will surely go to the head of the class. CAPTION: Picture, Scaled-down version of the grown-up blouson jacket in mocha nylon blend ($35) at Saks Fifth Avenue, worn with any favorite shirt and jeans.

"Brideshead Revisited" pastels for boys in a gray and blue tweed jacket with faint pink stripe ($72), pale blue, pink and yellow stripe dress shirt ($17), navy blue sweater vest ($15) at Bloomingdale's Boys Shop, teamed with a maroon, navy and yellow stripe knit tie by JG Hook ($9.50), also at Bloomingdale's.

Camel's-hair chic for the smallest of boys in this blazer by Imp ($85), dress shirt by Fino Fino ($34.50) and Gant brown wool slacks ($18.50), tie by William Taylor ($7.50) at Just So Children's Boutique (Foxhall Square).

Gray and white railroad stripes softened with a big white lace-trimmed collar and red ribbon tie ($34) by Marshall Sinclair at Woodward & Lothrop.

Shades of Charlie Chaplin in this black and white plaid bib-front shirt with bow tie ($20) and black corduroy suspender pant ($25) by T.C. & Co. at Hecht's.

Banker's pin stripes for a girl in a gray and white double-breasted vest ($17) worn with a pink shirt with white bib and tie ($19) and matching pin-stripe cuffed walking shorts ($18) by Russ Girl at Hecht's.PHOTOGRAPHS BY BILL SNEAD