I don't mean to sound snarky at all when I say this, but are there really that many times when you need to speak to the teacher and not just do the email thing? I understand a lot of people prefer face to face or voice to voice contact, but if you are really that hard to reach when the teacher is available, email sounds like your only option.

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OP here- to clear up a couple things-As I explained we do use email, and I have had 2 phone conversations this yr, so no it is not a regular occurance. The problem comes when I explain in what I think are clear terms about my son, and he ends up getting harmed because someone does not understand. He has a rare progressive disease. Sometimes explaining by email, when the person can't ask questions is difficult. When something has happened that they clearly did not understand, it shows we need to have a conversation. I have now told her I am available for a conference any day he attends school (scheduled part time due to disease) between 1-2 and am waiting to hear back. The problem is if it is a problem that should have resolution before he returns to school, it is difficult to wait for a planned conference. I will not take off work between 1-2 for a phone call that
may happen, and in the past other school staff has said they would call and it did not happen. So, I may be available, but if it may not happen I won't cancel clients for a possible phone call. There is nothing I can do about my son being with me in the a.m. He is ambulatory and can not be left unattended while I go in another rm to talk. No, there is not another adult. I will not discuss his prognosis or disease issues in front of him.
The bottom line question was, when something can't be fully explained by email, is it reasonable to think that a teacher would make a call after school hours if they were unable to reach the parent within a day, so that the childs needs can be met. Or, is it not a reasonable expectation and I should just deal with it and keep my son home until we manage to speak if necessary. He is very complicated and I know the school has not had this before. He is also on grade level, so belongs in a reg class. The teacher is not married and has no kids, as an fyi.
It has been interesting getting opinions. Unfortunately most of the suggestions have already been attempted.