The headteacher and the administrator have some authority here but they are clearly worried about the parent's power and so plot together and try to dismiss her, 'waste of time'. You can tell that they are a bit afraid because they say it 'very quietly'. The mother has come in to complain about the food that her son has to eat and although she is quite indignant she won't let her son say anything even though he ate the food!
Throughout the conversation we can see how each speaker's language differs from the others'.
The headteacher assumes an informal attitude with the administrator showing a bond between them which could be due to the fact that they are colleagues and know each other since they work together. However, when the mother comes in ,the headteacher takes a pause of 3 seconds to assume a formal and polite attitude after saying that the interview is a 'waste of time' very quietly to herself. When the parent complains about the food, the headteacher is quick to make it clear that she isn't at fault and is not the one to be blamed and hands over to her colleague.
Even though the administrator is in a more authoritative position compared to the parent he isn't very confident while talking. He pauses quite a few times where it is not needed to do so. This is further evidence of his hesitance. Also, he might be thinking of what to say to the parent, choosing the appropriate words to try to impress her. Furthermore, the administrator must be under pressure at moment of the conversation given that he has to please not only the parent, but the headteacher too. In fact, at very beginning when the headteacher orders him to 'get some really good facts' and 'throw her off', he only replied with a simple 'ok'. This shows that he has no other choice than to obey given that he has no authority against the headteacher.
The mother is authoritative as soon