Deaf individuals often have limited access to language during early life, and their delayed sign language onset can lead to later language deficits. Examining the effects of lacking early language in this population can help us better understand the role of early language in typical first language development. This talk focuses on the syntactic development of American Sign Language among deaf individuals with extremely late sign language onset, combining observations from three levels: longitudinal development, sentence processing strategies, and brain language pathways. Altogether, the findings from these studies suggest profound effects of early language deprivation on language development at the mono-clausal level.