This study contrasts two theoretical accounts that respectively interpret impaired grammatical comprehension in terms of impairment in an innate grammatical module and in terms of lower level problems with speech perception or deficits in phonological working memory, using comprehension data from subgroups of children with specific language impairment, with mild–moderate hearing loss, and normally developing children. It is suggested that limited processing capacity is the main determinant of deficient syntactic comprehension in children with specific language impairment.