Fab thread!!!
I feel nothing but gratitude and admiration towards the teachers at my daughter's school. They are truly fantastic, and I sincerely appreciate all the time, thought and effort that they put in, beyond the call of duty, to help our kids learn and to make school an enjoyable experience. I would love them to know that those efforts are seen, and that they are not taken for granted.
To the headteacher, I would say thank you for creating an ethos within the school which celebrates achievements of all varieties, which genuinely values diversity and which teaches the children to be really caring and supportive of one another. Not to mention an environment in which teachers clearly feel motivated and supported. I couldn't ask for my child to learn in a better setting.
I would like to thank all of the teachers at dd's school for being so warm and friendly (and knowing all the names of the children who they don't teach!) and for the extra time and effort that they put into all that they do - running clubs at lunchtimes and after school, preparing for school productions, planning special activities etc.
And to dd's wonderful teacher - gosh, where do I start! 
I would like to thank her for seeing and responding to my child as an individual, for catering to her particular needs and helping her to fulfil her potential, even though she has 27 other children to think about. I don't know how she differentiates work so effectively, but I know that she does it somehow, and that makes a huge difference.
I would like to thank her for the many, many extra hours that she spends in school each evening - planning, preparing and creating exciting learning opportunities for the children in her care. Her creativity astounds me, and her energy is incredible.
I would like to thank her for caring every bit as much about my child's happiness and her social and personal development as she does about NC levels and the numbers on which she, as a teacher, will be judged.
I would like to thank her for spending money out of her own pocket on things for the classroom and little extras to motivate the children in her class. I would like her to know that this is not expected, but it is greatly appreciated.
I would like to thank her for her patience, for managing to keep a smile on her face at the end of a day with 28 noisy five year-olds, and for managing to greet parents with a smile at the end of the day too. She must be exhausted!
We hear so much about teachers who aren't doing a great job, but I'm willing to bet that there are thousands out there who are!