The growth mindset, or the belief that intelligence can be increased with effort, has been shown to be positively associated with improved learning outcomes. This association has been observed in a few studies that inquired into reading outcomes, and fewer studies that looked into reading in a second language. The current study used data from the Programme for International Student Assessment (PISA) 2018 database to investigate the relationship between growth mindset and reading proficiency of Filipino students learning English. Data were from 6766 students who spoke a Philippine language at home, who were learning reading in English in high school, and who were assessed for reading proficiency using English texts. The study also inquired into the role of the students' socioeconomic status (SES) and controlled for some teacher-related and motivation-related variables. Results of hierarchical regression analysis showed a weak but significant positive relationship between growth mindset and reading proficiency. The relationship between SES and reading proficiency was stronger; more importantly, SES moderated the relationship between growth mindset and reading proficiency. The positive relationship between growth mindset and English reading proficiency became weaker as the students' SES decreased; the relationship was nonsignificant among students with the lowest SES. The discussion refers to SES differences in reading English language-learning environments in the Philippines and considers how resources in the learning environment enable (or constrain) the role of growth mindset in improving learning outcomes.