Plaid kilts are back in vogue. Sales of school uniforms rose 22 percent, reaching $1.1 billion last year compared with 1999's figure of $900 million, according to The NPD Group. The healthy blip doesn't come from kids heading off to private schools in droves. In fact, much to parents' delight, more public schools require, or at least allow, students to wear uniforms. Some 14 percent of respondents with kids in public and private elementary and middle schools say they have at least one child who's required to don a uniform. The survey of 9,000 moms with kids in kindergarten through the eighth grade showed that uniform sales represent 5 percent of the $20.4 billion children's apparel market. What do parents look for when making the buy? Not surprisingly, style isn't a major factor: 91 percent say fit, 90 percent say they value size availability, and 89 percent say they look for durability.