What is the most effective way to prevent students from cheating?

Recently, a group of students in Hanover, New Hampshire, broke into their high school at night to steal copies of upcoming Advanced Placement exams. The resulting scandal has turned national attention toward the prevalence of cheating in schools: A 2006 survey [2] by the Josephson Institute of Ethics, for instance, found that 60 percent of high school students admit to having cheated on an exam in the past twelve months. Can anything be done to curb these high numbers? Tell us what you think.