There's something wrong in my view if you can't get to see the head. At our primary school the head was always around at the start and the end of the day, and so if necessary you could just ask her there and then for an appointment. If he/she refuses to see you you ought to write to the chair of governors.
Just as an aside, I remember the year 1 primary class teacher coming into the playground at the end of one day to tell me in a loud voice that she had moved my daughter from the top table to the middle one in maths as she was struggling. I was most distraught due to the proximity of all the other parents collecting, and can't really remember how we fixed it, but we did. I think that the advice about just doing it all at home and ignoring what's going on in the class is probably the best thing - if the teacher and the head wont help .
But remember it's only year 1 - my struggling middle table daughter passed 11+ and went on to do A Level maths