I had this problem with the teachers at my son's school years ago, they insisted his attendance was poor and demanded an explanation.
I pointed out he kept catching cold and flu and that I would not send him in to school ill to spread it about, and that because he had a lung condition when an infant could not risk a cold turning into pneumonia.
I was told I was being ridiculous and "It's only a cold"
So I asked why I was speaking to the head of year and not the headmaster (principle in the US) and was told he was off sick with... a cold.

Incidentally their insistence that has education would suffer has proven equally fallacious as he is now an M.A. in English and is planning to go on to his doctorate as and when.