Two 6-year-old male fraternal twins each received 8 weeks of morphosyntactic and phonological intervention in counterbalanced order. Progress occurred for most targets and measures, with each child making greater progress for either phonology or morphosyntax during the corresponding unitary-domain block. Gains were maintained during the subsequent alternate treatment block. Possible indirect changes in the non-treated domain were also observed in global measures. The data suggest that at least some school-aged children with concomitant difficulties in morphosyntax and phonology, perhaps those with significant constraints in each domain, can benefit from sequences of unitary-domain intervention. This study invites further research concerning many unresolved clinical issues for school-aged children with protracted development in both phonology and morphosyntax.