Bonnie Walmsley remembers the kindergartners who arrived at her classroom 14 years ago. For most, it was their first experience of school. Some knew the alphabet and could count to ten. The rare student could read or write.

Today, Walmsley encounters a much wider range of abilities. Many children come in with more sophisticated skills, which she attributes partly to greater exposure to television and computers. Most have attended daycare programs. Some are 6-year-olds held back a year by parents who feared they were not mature enough for school. They share the kindergarten classroom with another population of children—5-year-olds who are still struggling to learn the alphabet and come from homes where literacy is not a priority.

"The gap has widened. There is a greater range of developmental levels now," says Walmsley, as she surveys her bustling classroom in suburban Clifton Park, NY. "I have one child who is doing multiplication and another who's still trying to identify numbers. It's become more challenging as a teacher."