High-quality afterschool programs (ASPs) are opportunities to diversify the ways that Latinx youth from economically underprivileged communities experience STEM learning. Utilizing qualitative methods, based on the experiences and perspectives of low-income Latinx middle school participants of a math enrichment ASP in Southern California, we identified four culturally responsive practices: (1) the promotion of an inclusive, safe, and respectful program climate, (2) engaging in personal conversations, (3) facilitating opportunities for mutual and math learning across diverse cultures and perspectives, and (4) the promotion of math and a range of social-emotional skills across contexts. These practices helped youth feel more connected to the program, their peers, and program staff (college mentors); provided a platform for youth voice and contribution to the processes of teaching and learning; facilitated opportunities for skill development and practice across the different contexts of youth's lives; interrelated with Latinx cultural values; and helped to promote youth's engagement and math learning. Importantly, youth's relationships with their mentors was a significant aspect of their experiences and perceptions of these practices. We argue that culturally responsive practices are necessary to achieve high-quality programs and provide specific implications for how ASPs can implement them in the design and implementation of their programs.