The relationship between ability to perform formal operatioans of Piaget and fifth craders achievement in science. The purpose of the study swas to find out the relationship between the ability to perform formal operations of Piaget and achievement in science. a number of 598 fifth graders of 12 elementary schools were invoved. Interview and test were used to collect the data which were then analyzed using statistics of percentages correlation analyses and multiple regression. The results indicate that girls are proportionally more able to perform formal operations than boys and that the ablity has positive relationship to students achievement in science