10th April 2018 From India, Salem
The reply provided by Mr Umakanthan is appropriate as per law. You submit your resignation and ask the management to release on date the three month notice is likely to be completed from date of resignation.
Please check whether any school manual is there in place where the policies are laid down.
11th April 2018 From India, Mumbai
If your appointment letter states three months' notice and not working days , then intervening holidays will be part of notice period.
It clearly looks like an afterthought by interpreting it as working day with malicious intent to prolong your stay.
You write to the authority that you have fulfilled the condition of the notice period of three months and you will walk away after its completion after completing due formalities.
12th April 2018 From India, Mumbai