Yes, I do think teachers are generally able to spot unhappy children. Since they spend so much time with their students, they tend to notice changes in behaviour, like if a child suddenly becomes withdrawn or unusually quiet. Many teachers receive training to recognise signs of emotional distress, and in some schools, there are even counsellors who work closely with teachers to identify and support these students. Plus, teachers often build strong relationships with their classes, so they can usually sense when something isn't quite right.