The nation's schools may actually do a better job than parents in keeping children fit and trim. A study found that 5- and 6-year-olds gained more weight over the summer than during the school year, casting doubt on the assumption that children are more active during summer vacation. The findings, which come as the issue of childhood obesity is gaining prominence in the US, do not reveal ＿＿（37）＿＿ is behind the out-of-school weight gain. The researchers guess it is because the summer months ＿＿（38）＿＿ the structure of the school year with its activities and daily comings and goings. Dough Downey, an Ohio State University sociologist who co-authored the study, said that for many youngsters, the lazy days of summer may offer ＿＿（39）＿＿ free time to eat snacks and lounge about watching TV or playing video games. He said the study seems to point to the need for parents to be more involved. It also raises the idea of a longer school year and more after-school programs to ＿＿（40）＿＿ children active. And schools should continue their efforts to promote good health, he said. "Clearly the source of children's obesity problems lies outside of the school."