how can we know he is listening or hearing ?

listening doesn't always means understanding personaly i listened to lots of persons what they said but not always understood what they where trying to say maybe they have a different sense of understanding that means that you as a speaker should try to expose what you're saying in many different ways so you could be almoust sure at least 90 precent of the listeners understand

People who are hearing or listening usually follow the speaker with their eyes. This means when the speaker moves of shifts position their eyes will also move. People with staring eyes usually have their minds somewhere else. So even if something happens in front of them they do not really notice what actually happened. Attentive students are the ones looking at the teacher, while absent minded students are the ones who stare into empty space. all the best in yout future lectures, rosdimy

As a student, I look at my teacher while she/he is instructing. That way i can listen very well to what she/he is saying, word for word..and if there are things that i don't understand, i ask. Students who just look at the teachers and don't bother to ask questions, they are just studying the teacher's look or appearance and do not understand and don't even care what she/he is teaching about. That's why i dont wonder if our teachers ask questions to those students who are just looking at them regarding the lessons they just taught and explained to us beause they are pretty aware that they dont listen. It is one way of testing the students' attentiveness and cooperation in the class. I remember my seatmate in my Econ class....Our teacher asked her a very simple question yet she didn't able to answer. What's funny was, she was not able to listen the question and answered the teacher with "Pardon Ma'am?". She simply was not listening the whole period.