The "Null", or "excluded" curriculum is a concept that was formulated by Eisner (1979) and consists on the amount of teaching material which is not covered, taught, nor included in the typical curricula of school districts.
The contextual significance of the null curriculum lies in the factors that cause the omission of concepts from a curriculum, particularly whether the omission is unintentional, or if it is blatantly biased. According to current arguments in education, an unintentional omission of certain topics does not hurt the overall academic preparation of students because students are taught to use their inquiry skills and natural curiosity to explore and discover new topics that are not introduced formally. In fact, according to Gehrke, Knapp, and Sirotnik (1992)
a null curriculum is powerful by virtue of its absence (p. 53)
Therefore, an unintentional omission does not have any negative impact on education, based on the argument that students are ultimately responsible for applying their inductive and deductive skills to conduct investigative experiences throughout their lifetime.
However, if a curricular omission is biased, the implication is that the curriculum designers could be operating under a specific agenda which, in turn, could signify that public education funding is being used inappropriately. The counter-argument to this notion is that, realistically speaking, there are many experts involved in the process of curriculum design. This keeps a system of checks that is balanced by curriculum standards. However, it is natural to question who has the last word to decide what is considered important, or not important enough, to be included in a teaching unit.
Overall, a null curriculum is whatever is not taught or considered for teaching, but such omission it is not indicative of a deficit in the process of teaching and learning.