It is the parent's responsibility to inform the school.
But a little TLC says a lot about the school.
My class ratio is 1:44. I have 2! Every class teacher will take the time to call. If you are sick, the teacher calls to find out if you are ok and if you are keeping up with your school work or if there is someone looking after you. If you're in a hospital, the teacher will organise a visit with your good friends to cheer you up. This is the norm. Sometimes it makes you wonder if the local system is all that bad. If we spoke Cantonese, I know where I'd be dropping my son off.
International school teachers are 'REALLY' busy with their smaller class sizes and shorter working hours. My son attends an international school and I don't expect his teacher to ring or drop an email and WOULDN'T COMPLAIN as that is just how it is but if she does, it's a plus and I recognise it as a bonus and he got lucky with his class teacher. And I would make sure the Principal knows that he/she has gem in his/her midst.