TOUGH SHELL.(The Talk of the Town)(DonorsChoose funds public schools)

Bill Gates may have donated fifty-one million dollars to the New York City public-school system this fall, but Amy Wallace's first graders still can't afford a new home for their pet crab, Clifford. Wallace, who is twenty-seven, teaches at P.S. 184, in the Brownsville section of Brooklyn, a school that is unable to provide her even with pencils and paper. A few days ago, she announced to her students, who were sitting cross-legged on the scuffed brown linoleum at the back of Room 201, "Today, we're going to be learning about hermit crabs. What do you know about crabs?"

Hands shot up: "If they pinch your arm, you can bleed!"; "They come from the South!"; "You can crack the pieces and eat the chicken inside!"

"Chicken?" Wallace said, smiling. "Hmm." She picked up a covered, clear-plastic dish and rested it on her lap. "I brought in a little friend of mine," she said. "His name is Clifford, and he's going to be our classroom pet." Three seashells, a sponge, and an empty baby-food jar were sitting on blue gravel at the bottom of the dish, and everyone pressed in close to look--and then shrieked as one of the shells suddenly arose, unfolding spiky antennae and hinged red legs.

"Sit on your bottoms," Wallace commanded as the children fled toward the corners of the room. "Jahrell, turn your body and stop squirming. Shanae, fold your hands just like I am." Once order was restored, she continued, "Do you think Clifford was born in that shell, Tabius?"

Tabius frowned, searching her face. "Yes?"

"What do you think, Shaquera?" Shaquera cautiously shook her head. "No--that's right. As it grows, the crab finds bigger and bigger shells to live in. Why? Tristan?"

"Otherwise, he might get squashed."