School shootings and child abusers may grab headlines, but violence against American children has dropped significantly over the last decade, new research finds. Surveys show that bullying and assault have both fallen by about a third, and sexual violence has dropped by 25 percent. Of 50 types of violence against children measured, 27 fell between 2003 and 2011. Researchers credit prevention programs, quicker response and better mental health care for both children and adults. But critics warn that the U.S. still has higher rates of violence than other developed countries.