SPEARPOINT by SYLVIA ASHTON-WARNER 224 pages. Knopf. $5.95.
"What about picking up your blocks, Henry?"
"I dowanna...and I don't have to."
"Well, who else is to pick them up?"
"Not me, you dum-dum!"
Once upon a time into the country of the doubly youngfive-year-olds, American five-year-olds, living like some future race at an experimental school in the Rockiesthere came an elderly stranger. She was doubly alien, a grandmother and a New Zealander. Yet Sylvia Ashton-Warner had her visas in order, even her special credentials. Or so she thought. Had she not written a book called Teacher...