This study examines what factors contribute to intercultural learning during the study abroad experience, drawing on Mezirow's theory of transformative learning and data from the Intercultural Development Inventory (IDI). Using data from 1,858 US students studying abroad in 27 countries over 6 years (2014-2020), this study constitutes the largest of its kind to date. Additionally, a powerful matching method is used to compare a sample of students enrolled in an Intercultural Communication and Leadership (ICL) course developed by the Council on International Education Exchange (CIEE) with a control group of study abroad students not enrolled in the course. Findings show that cultural mentorship via trained, skilled instructors is more important than other factors associated with intercultural learning while abroad. Furthermore, the findings highlight why international education faculty and administrators should advocate for study abroad in non-English-speaking locations and immersion in cultures that are more dissimilar to the dominant cultural context of US students. The highest learning potential in study abroad occurs when students experience heightened moments of cultural disorientation in unfamiliar cultural contexts and have experienced facilitators to guide them through reflection around intercultural differences.