Abstract: The pupils of three sections of the first year class are taken as the object of this study: one section as an experimental group and the two others as controlled groups (competitive in effect). In the experimental group, systematic observations and experiments were conducted in order to disclose the process and the different levels of understanding plus-minus applied problems of the first year pupils. And on the basis of the characteristics of each individual level, certain devices of instructions were employed in order to promoe their achievement. Results indicate: the process of understanding plus-minus applied problems are of five levels, they are correlated, yet, differentiated. According to the characteristics of each individual level, certain instructional methods were adopted, in consequence, the transference between different levels is accelerated, and the effect of ins ructions is evidently greater than any controlled groups under general instructional conditions.

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