WARWICK - About 40 students walked out of Warwick Valley High School at 10 a.m. Friday as part of an organized, nationwide effort marking the 19th anniversary of the Columbine High School shooting, in which 13 people were killed in Littleton, Colorado.Students from hundreds of high schools across the country were expected to participate in walkouts, part of a continuing wave of youth activism seeking tougher gun laws following the Feb.