He mainly contributed exploring the processes of courtship and divorce. He established the so-called principle of least interest, which states that the person who is part of the group, but is the one having the least interest of continuing with the relationship, is the one who has the most power over it. He applies the concept to personal, business and other types of relationships. In 1932, he published The Sociology of Teaching. He is described as an early classic in the field of education. He extended, for the first time, the idea of considering schools as organizations with an important social role.
Waller concluded that casual dating was a form of entertainment that had little to do with mate selection. Status attainment and excitement were at the center of the dating process, partners were selected based on status characteristics, for example good looks, nice clothes, and popularity.