Jeanne because I told my child (after thinking on it) something that undermined her teacher (which is why I thought long on it and talked to DH). I honestly thought it should be recognise and didn't want her learning a spelling that was not the usual one in the UK (I did tell her that reconize was not incorrect but is generally how they spell it in America).
This led to her sitting at the test and having to decide which to go with, me or the teacher, which was a difficult position for her at 7 with 2 adults she trusts to tell her good information.
She put recognise and so did a couple of her friends, they mark each other's papers this was marked wrong. She asked (smartarse!!!) and was told no it needs to be spelt as per the sheet and so they are wrong.
So she came home and told me this and I didn't want to cause any more difficulty for her and so just said "oh well then" or something else vague and gave her some food 
Anyway now I find out that I was wrong, really, to flag it. So I've caused her all that trouble, got her labelled a smartarse, got her work marked down, given her incorrect information, and undermined her faith in both me and her teacher! So all in all a really really shit result from one spelling.
So what I learn is, as mentioned, I don't know my arse from my elbow and need to not be confident that I know stuff as things I think are right may well not be
And
This whole smartarse thing I don't want her putting people's noses out of joint in the future, asking stuff like that, I have been encouraging her to ask, I should have thought to be more circumspect in that advice.