Previous research on the development of second language (L2) reading comprehension among adolescents and adults has looked at the relative importance of students' second language (L2) linguistic skills and home language (L1) reading comprehension skills in the development of L2 reading comprehension, with many studies finding a more important role for L2 language proficiency. However, the previous research has been done largely in foreign language settings with students who have age-appropriate reading skills in the L1. We extend the question of the relative importance of L1 reading skills and L2 language proficiency to L2 reading comprehension to Spanish-speaking adolescent newcomer emergent bilinguals in New York City with low levels of L1 reading, as research on these students is lacking and little is known about their development of L2 academic skills. We find that for this population L1 reading comprehension plays a significant role in L2 reading comprehension equal to, if not greater than, L2 language proficiency. These findings suggest the need to include continued support of L1 reading skills in order for reading in the L2 to develop, at least for newcomer students with low literacy skills.