i agree with you wholly artyfishymeau.
now let's see.
Teacher's have a workload agreement negotiated with the gov't and all the unions. It states that teachers do not have to do administrative tasks such as writing letters home. it is the job of a secretary.
If you go and correct a teacher - it should be the secretary's mistake. Not hers. I agree that all secretaries should also have perfect command of written English too and type correctly. But it ain't going to happen before any of us retire. Now would a teacher look at you and say, it wasn't my mistake, it was the secretary's? Not likely. So now you have undermined her for something she didn't do.
Secondly, if all pieces of correspondence home had to wait for a secretary to type, that would just be laughable and that is another thread more suited for a teaching messageboard.
Now, let's assume for a moment that this teacher actually wrote this note herself since it is most likely she did otherwise it would not get home in time. She made a mistake she shouldn't have and it would grate on my nerve equally and make me think all sorts about the dumbing down in education and possibly about the gov't paying peanuts so get monkeys, etc, etc..
Did it impact on the meaning she intended? Did it impact on your dd's learning? Is it endemic in what she does and you know this because of frequent interaction with her i.e, you see her in the classroom often enough to know this?
Do you know what kind of day she had and what she is coping with at home? Are you in the position to, in this instance, teach her how to use apostrophes properly as a part of your conversation or to arrange with the board of governors to have a general INSET for all staff at her school on the fundamentals of grammar?
If you answered 'no' to some of these then all I can see you doing is undermining her. This kind of mistake and knee jerk reaction by parents is the sort of attrition that teachers have in their day to day lives. The one little pointing out is insignificant and she may be able to take it on the chin, laugh and get on with life, even be grateful for your well intentioned assistance but after years of attrition, it makes teachers jaded and unenthusiastic to say the least.
It can make her say in th long run, balls to christingle, a day out to the museum, panto, etc. I don't have the time to write letters. It is not part of my job. (knowing how slowly the turn around is to wait for a secretary to do it) I can only see the children being poorer for it, not the parent.
I say these things as a holder of degrees in English and Linguistics. I have taught English and I'm currently teaching two foriegn languages in the UK. English is not the language I spoke at home while growing up. My first language is a language which is unwritten and threatened with extinction.
I would love primary students to come into secondary school with a competence in grammar as it would make their second language acquistion so much easier. It ain't happening and I accept that. I also accept that the majority of adults inside and outside the teaching profession do not have a satisfactory command of the grammar of their own language.
So if a teacher's mistake is not crucial to the facts that my child needs at the time, I wouldn't point it out to her. I have bigger fish to fry and so does she.
PS. I love it when my Yr8 Set 3 boys point out a mistake I make as they are doolally as anything. It tells me that they are enthusiastic and in tune.