This paper presents results from two studies, each looking at the development of reading comprehension in English as a second language (L2). The studies include a population of learners who have not often been included in L2 reading research, namely Spanish-speaking adolescent newcomers to New York City. Many of these students received limited or inconsistent education in their home countries before entering the U.S. school system in the upper grades. Thus, adolescent newcomers have a range of academic skills in their 1st languages (L1) upon entry to U.S. schools, and little is known about their development of L2 reading. The studies reported here address important questions about the role played by the L1 and include participants with low levels of L1 reading in order to get a comprehensive view of the development of L2 reading among adolescent emergent bilinguals. Study 1 looks at the relative contribution of L1 reading comprehension and L2 linguistic knowledge to L2 reading comprehension. Study 2 does a more in-depth analysis of the role of L1 in L2 reading by exploring the contribution of L1 morphological awareness to L2 reading. Study 2 considers mediating variables such as L1 and L2 reading vocabulary and L2 morphological awareness in L2 reading comprehension. Together, the studies find that L1 reading comprehension and L1 morphological awareness do play crucial roles in the development of L2 reading among adolescent newcomers, above and beyond that of L2 vocabulary alone.