In 2004, Second Step (Committee for Children, 2002), a violence prevention program, was implemented in the Cleveland Heights-University Heights school district for 1,416 K through second grade students. Both process and outcome measures were used to evaluate program impact and examine issues related to the implementation and evaluation of evidence-based practices. Process measures indicated a high level of implementation fidelity, while pre/post outcome testing on a 20% random sample of students demonstrated significant reductions in reactive aggression scores, t = 2.221, df = 238, p less than 0.05, and evidence of declines in proactive aggression. Authors discuss challenges and opportunities related to implementing and evaluating evidence-based programming in Safe Schools/Health Students sites, particularly regarding strategies for the assessment of differential intervention effects to evaluate program outcomes. (Contains 4 tables.)