We investigate literacy as one possible factor that influences language development in 9-10-year-old Spanish heritage speakers, and how this leads to the end state linguistic competence. Our Literacy Enhancement Hypothesis states that learning to read and write strengthens morphological representations, which aids processing by improving the parser’s ability to monitor and integrate morphosyntactic features. This presents consequences for L1 processing in HSs who develop literacy skills in L2 English, which is morphologically less complex than Spanish. This variation in home and school input could have a severe impact on L1 development. Thus, we ask (i) how literacy in Spanish HSs influences their ability to use linguistic cues while processing complex syntactic structures in Spanish, and (ii) if they show similarities or differences when compared to low and high literate L1 Spanish-speaking adults. The experiments in this study manipulate word order, gender morphology, and plausibility to investigate how literacy affects the comprehension of verbal passives. Experiment 1 uses an off-line picture-matching task testing comprehension of passives in Spanish while Experiment 2 uses eye-tracking to test if HSs in bilingual schools and high literate adults are more effective than HSs in English-only schools and low literate adults at using morphosyntactic gender cues to anticipate the theme of (im)plausible sentences. This provides psycholinguistic data in considering specific features of linguistic knowledge that may cause heritage speakers (and low-literates) to have trouble while parsing complex sentences. These experiments have the potential to inform us about how literacy influences the cognitive resources different types of comprehenders use to parse complex syntactic structures in Spanish. Not only will the results inform our understanding of how passives are acquired in heritage Spanish, we will also see in what ways this interacts with processing.