In school bullying, witnesses play a fundamental role because their defensive reactions can stop bullying situations. However, a great majority of witnesses remain passive despite their prodefense personal beliefs. To address this gap between witnesses' beliefs and behaviors, we developed and tested two social psychology strategies, namely, the induced hypocrisy and implementation intention. In an experimental and longitudinal study (N = 101), we randomly divided 7th- and 8th-grade students into three conditions, namely, control, induced hypocrisy, or implementation intention. Linear mixed models showed that the two strategies immediately increased planned defending behaviors as well as self-reported defending behaviors at three months but with a stronger effect at three months for the induced hypocrisy strategy. These new prevention avenues for practitioners are discussed according to current approaches.