TUESDAY, April 30 (HealthDay News) -- Smoking prevention programs in schools do work, reducing the number of children and teens who later become smokers, a large new review found.

Investigators analyzed data from 134 studies that included a total of more than 428,000 participants, aged 5 to 18, in 25 countries.

Some types of programs were more effective than others and, overall, kids who had already started smoking didn't seem to benefit.

Among youngsters who had never smoked, anti-smoking programs in schools did not have significant effects within the first year. However, over a longer period of time the number of smokers was significantly lower among those who had smoking prevention programs than those who did not.

When the review authors focused on a mixed group of youngsters who had never smoked, had experimented with smoking and had smoked and quit, they found that anti-smoking programs in schools had no long-term effect.

Some of the anti-smoking programs helped students develop social skills or taught them to resist social pressure to smoke. In the long term, programs that promoted social skills or taught social skills in combination with tips on how to resist pressure to smoke had a significant effect on preventing smoking in youngsters who had never smoked.

No benefit was seen in programs that focused solely on resisting pressure to smoke or on those that used information only or that combined tobacco education with wider school and community initiatives, the review authors said.

Anti-smoking program booster sessions had no effect on the number of young people who later took up smoking, according to the findings published April 29 in The Cochrane Library.

"This review is important because there are no other comprehensive reviews of world literature on school-based smoking prevention programs," review co-author Julie McLellan, from the department of primary care health sciences at the University of Oxford in England, said in a journal news release.

"The main strength of the review is that it includes a large number of trials and participants. However, over half were from the U.S., so we need to see studies across all areas of the world, as well as further studies analyzing the effects of interventions by gender," she added.

More information

The U.S. Centers for Disease Control and Prevention has more about youth and tobacco.