In a video linked here (start at minute 38:46) Harvard Professor and Validation Team Member of the Common Core State Standards Dr. Catherine Snow makes the case that the vocabulary deficit that plagues highly impacted students is as much a content knowledge deficit. She goes on to assert that systems need to be strategic in remediating the issue by providing students access to a content rich curriculum (minute 39:59).
At minute 48:31 Dr. Snow describes the type of curricular supports teachers need to assist children with vocabulary acquisition. She is specific in noting that curriculum should be seen as a support instead of a constraint and that when curriculum is well designed, time is available to extend learning.
You can review the entire video here.