@Itwouldtakemuchmorethanthis
Hi, sorry to jump on your question but I just wanted to put my thoughts in too.
In my experience, teachers have a pretty good idea of when something isn't quite right with a child, be that academically, behaviourally, socially etc.
They don't always have the in-depth knowledge to pinpoint an exact condition but are able to flag up a concern early on to allow support to be put in place.
They would then liaise with the SENDCo and do their own research to effectively support the child as well as take on any advise from external agencies.
You're correct in saying that they can't possibly teach the child if they aren't aware of their needs and so it is the responsibility of the teacher to seek advice and research where they can.
I have teachers who regularly ask to go on training to further their knowledge, particularly if they have a child with specific needs.
I'm sure this isn't the case everywhere but my experience is that most teachers can identify a child with additional needs, especially in early years because they know where a child should be developmentally so can spot discrepancies.
Sorry if none of that makes sense! 