This study identifies factors predicting reading literacy achievement among Grade 4 students in South Africa by utilizing Vygotsky's social interaction theory. The study draws on the preProgress in International Reading Literacy Study (prePIRLS) 2011 data, which places South African Grade 4 students' results below the international centre point of 500 at 461. For the current analysis, distinct items from the prePIRLS 2011 parent, student, and teacher questionnaires predict learning outcomes significantly, including parents talking to students about school and assisting with homework, teachers' degree of success in implementing the school's curriculum, and student responses on how clear teacher expectations are. Findings explain 41% of the variance in student reading achievement and provide evidence for the significant role of teachers and parents in predicting increased reading literacy achievement scores. An absence of interaction with the child in either parents who do not engage in homework activities or talking about school, teachers who do not successfully implement the curriculum or make their expectations clear to students link statistically significantly to lower reading literacy achievement scores. Achievement for Grade 4 students who were tested in African languages was adversely worse than those students by test language.