This study explores whether there is a heterogeneous effect of high school college counselors on college application and enrollment. Most research on the impact of counselors has focused on the effect of traditional school counselors and not on high school college counselors, individuals whose primary responsibility is to assist students with application and selection. This study builds on a small vein of research that explores the effectiveness of high school college counselors. Research demonstrates that though application and enrollment in college have increased across the United States population, students with low-income and prospective first-generation college students still lag behind their higher-income and continuing-generation peers. Evidence supports that lower-income and continuing-generation students have different information, thoughts, and beliefs about college. Explanations for why these differences exist are theoretically tied to social and cultural capital. For some students, information and support provided by the high school may fill a critical gap in the knowledge and expectations related to college going. This study sought to determine whether college counselors have a differential effect across varying social and cultural capital levels. The study incorporates a causal analytical design, inverse probability weighting, with specifications for effect modification to determine under what conditions an effect is significant. Results show limited evidence of the effectiveness of college counselors in high schools across all moderators. There is some support that prospective first-generation students have an increased probability of enrollment in college if they attend a school with a high school college counselor. Limitations of this study, recommendations for policy and practice, and directions for future research are discussed. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]