In a classroom, if a teacher writes a topic on the board and asks the students to help him organise related words and concepts in a cluster around the central topic, what is the teacher doing?

In the case of a teacher dealing with a large number of students in a class, which method would work best?

When teaching Environmental Studies (EVS) or Science, how can a teacher best ensure that a student with hearing impairment understands a complex process like the 'Water Cycle'?