'How can a pupil think about maths when that sort of stuff is going on?'
Sometimes a child falls asleep in class and other pupils are eager to bring this to the teacher's attention, but TJ Clare (right) responds gently and tells them: "That's okay."
He knows that the child may not have had a decent night's rest in the single hotel room where he lives with his family since they became homeless and that he had been up early to make the long journey to school from a new address.
"They come in shattered. Do you allow them to sleep? Yes, as a teacher, you take responsibility," he said.
Or there might be a pupil whose thoughts are miles away and Mr Clare recognises another tell-tale sign of a child living in emergency accommodation.
"We might once have called it daydreaming, but they are taking a break in their heads" - a break, he says, from the reality of disrupted lives.
He gives the example of the family who were evicted a couple of weeks before Christmas and whose life in a hotel also involves not being able to cook their own meals.
Mr Clare teaches second class in a boys' primary school in Blanchardstown, west Dublin, an area where large numbers of young families are renting, and, as a consequence, the risk of homelessness is high.
Tyrellstown is in the school catchment area and he is dreading to see what effect the threatened eviction of more than 200 families in a local housing estate will have on pupils.
There are sensitivities too around teaching when the subject of home comes up because, he says, "textbooks don't cover emergency accommodation".
Gregor Kerr teaches fifth class in north inner-city Dublin and also comes face to face with homelessness in school. He worries about the long-term mental health of children.
"Not being able to bring friends home is very hard for a 10-year-old," he said.
He spoke of one family who, having brought their children to school, returned home to find their bags had been packed and they had to leave their accommodation.
"How do you sit in class and think about maths when you have that sort of stuff going on?"