Question

A study that examines how elementary school children form cliques on the playground would constitute

Answer 1

It would constitute Micro-level research. 
These levels pertain to Bronfenbrenner's ecological systems theory, there are 5 main levels, the one in question is the microsystems level or the groups and institutions that directly impact an individual, in this case, it is the link between an individual and its' peers. The other levels present in Bronfenbrenner's ecological systems theory are: mesosystem (interaction with the different microsystems, crossing interactions, ex: the interactions between school and home, the teacher and parents, peers and home, peers and parents, etc), exosystem (broader influences that an individual doesn't necessarily control or even participate in that still affect their lives, ex: schools, local government, religious institutions, etc) macrosystem (cultural context, values, patterns) and chronosystem (sociohistorical circumstances).