Abstract: The aim of the research was to analyse the processes of learning rational number in algebra by 5-6th grade pupils aged 13-14. Three experiments were performed. The results obtained throw light on the characteristics of the processes of grasping the conception of negative number by the pupils, on the interrelation between the abstract and concrete thinking, On the ability of verbal accounting and on the speed and accuracy of calculation. The authors were of the opinion that it is feasible the 5th grade pupils begin to learn rational number, and suggestions on teaching program in educational reform were made.

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