High school underrepresented minority students in the US are at an increased risk of dropping out of the STEM pipeline. Based on expectancy-value theory, we examined if Latino students' perception of support from parents, siblings/cousins, teachers, and friends in 10th grade predicted their science ability self-concepts and values, which in turn predicted their classroom engagement. Survey data were collected from 104 Latino high school students and their science teachers. The findings suggest that adolescents' perceptions of overall support and home-based support predicted adolescents' science ability self-concepts at 10th grade while controlling for their 9th grade self-concepts. Although adolescents reported high support from teachers, teacher or school-based support alone was not a strong correlate of their motivational beliefs. Perceived support was indirectly related to classroom engagement through adolescents' ability self-concepts. Feeling supported across home and school may be necessary to sustain adolescents' science motivational beliefs and, in turn, their science classroom engagement.