The educational external efficiency is viewed as the accountability of the educational system in various personal, social, economic and political aspects, which by understanding factors affecting the development of its status, it is clear that the reason for the non-fulfillment of the functions of education in a society is affected by qualitative and quantitative issues of education or lack of educational equity and institutional quality. Understanding the factors allows a country to be able to control most functions of education achieved without more abundant economic resources allocated to the educational system. This paper measures the efficiency of production process of education in Iran during 1972-2013 using a semi-parametric DEA input-based with constant returns to scale, and is able to identify surplus and shortage of inputs and outputs on inefficient units. Then, there are three steps to identify determinants of efficiency status. The first is a sensitivity analysis of efficiency in order to prioritize the inputs in efficiency, secondly, the separation process of the formation of the efficiency of external education into two sub-processes, in which first process efficiency (turning education into knowledge) is under internal efficiency of education and second process ( turning knowledge into understanding) under the title of knowledge efficiency and thirdly, using time-series regression methods to examine the effects of "environmental factors" on the efficiency of external education. The results show that the external efficiency of education is achieved in 87% of the years studied. The high-output deficiency in order of importance in the external efficiency is related to production, environmental sustainability, productivity, stability and security of the family and the highest surplus is in expenditure on education and per capita teacher for per student. The major source of inefficiency is related to the second process, i.e, the process of transforming knowledge into understanding. Environmental factors of internal efficiency of education, knowledge efficiency, employment rate and economic independence, have a significant positive effect on the external efficiency of education and

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