Explain why education is a new academic discipline for Durkheim?
It is arguable that sociology is much more likely to be linked to Durkheim as a "new academic discipline" because he established sociology as a discipline himself, as he is considered its top representative.
If your question is still about education and Durkheim, then the argument would move toward the fact that the sociologist sees education as a manifestation of sociology and, as such, would be considered a new academic discipline that grows, changes, and transmutes consistently the same way that society does over and over.
On Hoenisch's Durkheim and Educational Systems (2005), the author writes that Durkheim viewed education as a microcosmic, or better yet, as a parallel universe of society. This is because society builds its educational systems. It is society that intends to replicate its values, knowledge, information, and history within the confines of education. This is done not just to preserve society itself, but also to establish parameters of knowledge and information that should be shared from generation to generation.
As such, Durkheim offered also that society creates models, including those of behavior, based on what the ideal human should be like. These models also intend to explain how the dynamics between man and society should be.
Moreover, Durkheim believed that the educational model should be viewed as a social "constraint". The term "constraint" is not used in a negative way. Instead, it means that, through a teaching model, society will impose upon its least educated individuals the rules, ethics, and expectations that will mold them. Sociology and education are therefore interconnected because the individual would never learn an ideal model of social and ethical behavior on his or her own. The educational model is therefore the conduit through which sociology will be taught and modeled.
Since society changes by the second, so does education and the models that will teach sociology from the inside out: through social studies, ethics, law, psychology, social sciences and sociology as a philosophy. These constant changes would make education a dynamic and constantly changing discipline that, by all parameters, will consistently be "new" in both form and content.