During two jears was being studied the annual dynamics of the final products of metabolism of protein - ureas and creatinin, and the dynamics of Na и K among pupils of the first form educated according to different pedagogical programmes. In the course of investigations had been revealed the dependence of the level of excration of criatinin and K from the form of organization of the educational process that allows to use this factor as a criterion of the functional tension of the systems of an organism during the adaptation to school or as a criterion of the evaluation of "the cost" of educational activity at the period of development of initial tiring.