Factors in language development, birth to age seven

This longitudinal study of nearly 2000 children found that the effect of early life and home factors are clear in the early years, but that these “…have played out by age 4.” They also found that “…language abilities are more stable between 4 and 7 than between 2 and 4 years.” Meaning, it’s easier to know if a child will persist with a language disorder by measuring skills at age four than by measuring skills at age two (which many of us have figured out, clinically).
Also, the quality of life was found to be particularly low for the seven-year-olds with low language. These children “…experience significant limitations in school and psychosocial functioning at twice the rate reported in peers with typical language,” including low literacy skills and social–emotional and behavioral skills. Further, the authors state, “Health-related quality of life (HRQL) was measured on the parent-reported Pediatric Quality of Life Scale and “limitations” in HRQL were defined as scores falling ≥1 SD below the sample mean, a level found to be similar to that of children with severe or chronic health conditions such as rheumatic conditions and newly diagnosed cancer in a large population sample.” They state, “…it is a significant concern that children with low language were experiencing (HRQL) limitations at more than twice the frequency reported by their peers with typical language.”
 
McKean, C., Reilly, S., Bavin, E.L., Bretherton, L., Cini, E., Conway, L. Mensah, F. (2017). Language Outcomes at 7 years: early predictors and co-occurring difficulties. Pediatrics, 139(3).