Recruiting schools and kids to participate in drug prevention evaluations is no longer, if it ever was, a "done deal." Since the mid-1980s, schools have been inundated with requirements for drug programs and requests to cooperate with program evaluations. As a consequence, both treatment and control schools are harder to find. In addition, many school administrators feel that their students have been "overstudied" and parents often look askance at questionnaires that seek information on sensitive topics such as drug use. Even if evaluators successfully pass the "recruitment barrier," additional problems such as the loss of schools or study participants over time may threaten the study's integrity. This paper examines the challenges facing evaluators of community-based programs when the design calls for assessing prevention efforts targeted at children or adolescents in school. It discusses the barriers to recruiting schools for the evaluation and keeping them in the study over time, and presents alternative strategies for overcoming these barriers. It then turns to the problems of getting and keeping student participants, focusing, in particular, on strategies for obtaining parental consent and minimizing attrition over time. (Contains 2 tables and 24 references.) (Author)