Persuasive technology is a sub-discipline of Human-Computer Interaction that has emerged within the last 10 years, and which has generated increasing interest in the application of persuasion to systems design. Most applications have to date been developed in commercial contexts, as well in the domain of health promotion. We present a mainly theoretical consideration of how persuasive technology could be used in educational contexts, particularly in school settings. We consider how persuasive technology design may need to be modified to meet the needs of complex educational settings. We propose four design principles for the use of persuasive technology in instructional design, including credibility and Kairos. We derive these from theoretical considerations, as well as from our experience with the HANDS project, which has developed a mobile persuasive application for positive behaviour change in young people with Autistic Spectrum Disorders. We conclude that persuasive technology has the potential to be used effectively to bring about positive behavior and attitude change in school settings.