"There's increasing evidence that children gain a lot from going to preschool," says Parents advisor Kathleen McCartney, PhD, dean of Harvard Graduate School of Education, in Cambridge, Massachusetts. "At preschool, they become exposed to numbers, letters, and shapes. And, more important, they learn how to socialize -- get along with other children, share, contribute to circle time."

Statistics show that a majority of kids attend at least one year of preschool: According to the National Institute for Early Education Research (NIEER), more than two-thirds of 4-year-olds and more than 40 percent of 3-year-olds were enrolled in a preschool in 2005. "Children who attend high-quality preschool enter kindergarten with better pre-reading skills, richer vocabularies, and stronger basic math skills than those who do not," says NIEER director W. Steven Barnett, PhD.

"Every child should have some sort of group experience before he starts kindergarten," says Amy Flynn, director of New York City's Bank Street Family Center. Music and gymnastics classes are great, but what preschools do that less formal classes don't is teach kids how to be students. Your child will learn how to raise her hand, take turns, and share the teacher's attention. What's more, she'll learn how to separate from Mommy, who often stays in a music or gym class. All of this makes for an easier transition to kindergarten. "Kindergarten teachers will tell you that the students who are ready to learn are those who come into school with good social and behavior-management skills," Smith says.