Interdisciplinary teaching is a method, or set of methods, used to teach across curricular disciplines or "the bringing together of separate disciplines around common themes, issues, or problems.” often Interdisciplinary instruction associated with or a component of several other instructional approaches. For example, in a review of literature on the subject published in 1994, Kathy Lake identified seven elements common to integrated curriculum models: a combination of subjects; an emphasis on projects; the use of a wide variety of source material, not just textbooks; highlighting relationships among concepts; thematic units; flexible schedules; and flexible student grouping.