Smoking among U.S. high school students has declined by nearly one-fifth since 2000 but has not budged among middle-schoolers, according to a study released Thursday.

Nearly one out of four high school students, 23 percent, said they had smoked tobacco in the preceding month -- a drop from 28 percent the last time the survey was conducted, two years earlier.

About 13 percent of middle school students said they had smoked, about the same as in the previous survey.

The spring 2002 survey questioned 26,119 students at 246 schools. The survey is conducted every two years by the Washington-based American Legacy Foundation (search), which is funded by the nationwide tobacco settlement (search).

"The reason it has gone down is a combination of factors, from the increase in cigarette prices to the passage of more smoke-free laws and policies," said Cheryl Healton, president of the foundation. "Among middle-schoolers, they tend to be experimenters and not daily smokers yet."

Healton also credited anti-tobacco advertising campaigns with discouraging teenagers from smoking. She said more effective efforts may be needed to reach students in grades six through eight.

"It makes me wonder if the declines we've been seeing are going to start to plateau," said Dr. Corinne Husten, a medical officer with the CDC's Office on Smoking and Health (search).

White students were more likely to use cigarettes than black, Hispanic or Asian students.

Overall, Asians smoked less than students of other races. Among middle-schoolers, whites, blacks and Hispanics smoked at roughly equal rates, while in high school, whites smoked more than other students.