The Critical Period of Intervention (CPI) model for drug prevention in the schools is unique in that its underlying rationale rests on psychological principles, particularly with the concepts of stage developmental theory and critical period theory. The focus of this program is on prevention, not rehabilitation. CPI consists of four phases: identification, diagnosis, intervention, and evaluation. The purpose of the CPI paradigm is not only to identify the potential high-risk students but, more importantly, to constructively intervene at the critical persuasible moment providing practical and concrete forms of helping. (Author)