The sand-and-water table in Barry Hoff's classroom in the Southampton Head Start program on New York's Long Island, used to be filled with sand on two sides.

But water was restored to the table last month as 16 preschoolers stood around it, dipping and pouring water through tubes and funnels, squeezing it through turkey basters, and learning, in the process, something of what it's like to think like scientists.

The change in Mr. Hoff's room, and in a handful of other classrooms like ...