Ming (Agents of Speech) explains the difference between language delay and language disorder. In this segment Ming defines language delay as a slower-but-typical developmental trajectory that often catches up depending on severity, and warns that even modest delays (e.g., six months to a year) can reduce social interaction opportunities and become a risk factor for later academic difficulties (reading, writing).
In terms of language delay or disorder. Delay means that everything looks normal, typically developing, but it's just slower. So language delays usually do catch up, but it really depends on the severity again, because if your child is three years old and they're like six months behind in terms of language, think about how much less opportunities they will have, how much less fruitful social interaction they can have, how much friendship they can build if they are six months to a year delayed. And therefore this whole effect will carry forward. And that's why we see it's just reality, that children who are language laid will struggle, and it becomes a risk factor that even academics reading, writing becomes hard for them. And this is not anyone's fault or the system's fault or whatever.
