Hi LFFFTA. From the other thread you'd said that you definitely know you're not there to diagnose anyone, but would like to help spot when a child may need an assessment.
You're right that teacher training rarely covers any SEN at all. In a Council meeting about this recently, the assembled teachers said that the most they'd ever been given in training was a half day on the subject. Given that 1 in 7 children in their classrooms may have a disability of some kind or other SEN (and it's 1 in 4 in the primary school where I'm a Governor) this is just appalling. These children often need a different teaching technique if they're to succeed and the teachers are being given NO way to help them.
Whilst some parents might not appreciate the teacher thinking their child might have a disability/SEN, my own son went through absolute hell at the hands of teachers who said "of course there's nothing wrong with him - he's just not that bright and messes about in the class too much". Nope. Three specialists all confirmed he has quite profound dyslexia. He's 16 and (for example) can't spell his own name or use a dictionary to find a word, despite an IQ in the top 2%. After a meaningless and exhausting battle in the last school, ended up having to pay privately to undo the damage and give him a chance. Most kids don't get that chance. They need teachers who can spot basic problems and know who to ask for help.
So...useful info on Teachernet in the SEN bit. Government info pack came out last year on Dyslexia - the SENCO should have a copy. This year there's info coming out about autism, so watch out for that too.
Nip onto the websites for the main charities for the disabilities - there's nearly always links to basic info about the disabilities on there and how to spot them in a particular age of child.
Definitely involve the SENCO in any concerns you have, though not all of them have training in disabilities as yet until the new rules come into play this year. (No, really. Most are excellent, but some are appointed because no-one else wants to do it). I was in a school recently where one lad was displaying absolutely classic signs of a disability, but the SENCO hadn't any knowledge of that disability at all so hadn't even though to flag it up.
I was watching a programme on the tele last night about badly behaved children and thinking "Well, that's a child who seems to be on the autistic spectrum - wonder if they've ever been assessed for it?". Probably not. They're probably classified as badly behaved instead.
Quick tip:
Boys: Will tend to misbehave if they're not coping due to a disability/SEN.
Girls: Will tend to sit in a corner and do almost nothing if they're not coping, or get someone at home to do their homework for them, so get missed from most diagnoses as no-one thinks to check the ones who are well behaved and who seem to be handing in something.
Definitely don't try to be an amateur psychologist. But knowing what to look for is a huge help in any classroom.