CAP (College Ambition Program), is a whole-school intervention designed to provide college access to low-income and minority students in public high schools has been in the field for four years.  The program, funded by the National Science Foundation and the Michigan Department of Education, provides support and resources to students and high schools through a variety of different avenues, including course counseling and advising, tutoring and mentoring, financial aid planning, and college visits.  This paper presents findings from a mixed-method multi-site randomized controlled trial of the school-wide intervention.  It discusses the methodological and implementation challenges CAP has experienced and their implications for scaling the program. Results suggest that the pathway to scale-up requires recognition of unexpected within school variation and what potential such variation can mean for replication across multiple sites.