Social Services have way more cases on their books than they can deal with adequately now, without going and looking randomly for more cases.
Random investigations would also cost a huge amount of money and Social Services are renowned for being strapped for cash.
Schools are hyper vigilant on reporting cases of suspected abuse and they all get followed up. We have special forms printed on bright cat-sick-yellow paper so that they stand out. I have reported about 10 cases of suspected abuse in the last year.
One instance that was quite amusing was when a child in my previous school had some nasty scratches on her upper arms. She took her cardigan off and I saw the scratches and I asked her how she got them. She said the family dog had jumped up on her and scratched her and she complained that I was about the seventh teacher to ask about the scratches. I was amused because it showed how aware all the teachers were and how we all asked her in such a way that she wasn't put on her guard as to why we were concerned.
A deep concern is when you ask a child why they are upset and they reply that mummy or daddy has told them not to tell anyone about it. Children actually find it really hard to keep secrets and will eventually spill the beans because they are upset and you are offering consolation.
Children love to share and to tell people things. Teachers get told all kinds of private and personal things that you may not even be aware your child knows.
Although we would never tell a parent what we know, we quite often have a chuckle over some of the things the kids tell us.