A Case Study On The Elementary And Secondary School Pupils' Development Of Ability Of Control Variables

With the development of the 8th compulsory educational reform and the carry-out of science inquiry-oriented teaching & learning, teachers and students feel that there are many difficulties during science inquiry-oriented teaching & learning, especially in the part of designing experiments which include several dependent factors. It is very hard for students to ensure and control more than one variable. So it is very instructive for teachers to design inquiry activities, to select different content for students of different grades and improve science teaching so as to study the development of ability of control variables and its psychology base. The ability of control variables -----as an important inquiry ability-------plays a very important role to for students'inquiry study, it plays an important role for students'excessive learning and problem-solving after they come into society. Based on Piaget'study, this study designs two tasks-----one is "which ball jumps higher?"the other is "which ball runs faster?", and uses the method of clinic interview to examine the students who range from the first grade to the seventh grade, and have never studied pendulum in physics class, to make sure their different levels of development of ability of control variables, to seek whether the degree of familiarity on the task will affect the students'performance. Through analyzing the students'performance, we find that there are three stages of the development of control variables: no consciousness of controlling variables Cannot isolate correlated variables having consciousness of controlling variables (this stage includes two sub-stage: the controlling variables based on the "combinatorial system"the controlling variables based on the schema "all other things being equal". With the increasing of age, the number in stage one decreases rapidly, which is true to the second stage. At stage three, the number of students increases sharply with ages going up. There is a rapid increasing period in the two experiments, but they are in different ages. In experiment one, there is a rapid increasing period between the third grade and fifth grade, and in experiment two, the period is between the fifth grade and seventh grade. In experiment one, half of grade five and grade seven reach the stage three, and in experiment two, until the seventh grade that half of students reach the stage three. All of these findings results from the different task in two experiments and the degree of familiarity to the two experiments. At the same time, the students who are in the concrete level can deal with problems in an actual,concrete,direct way by using the strategy of controlling variables. Given students'ages and performance, in the research, the limitation of cognitive level is the factor that influences students'development of ability of control variables, and the performances of every grade in the two experiments show the limitation, and the criterion which divides stage three into two sub-stage is the difference between the concrete operation and formal operation. The next, from the psycho logic point of view, this paper further analyzes students'development of ability of control variables and compares the conclusion with the others'studies. This author thinks that the cognitive development of ability of control variables ascends gradually; students'development of ability of control variables has not an absolute boundary between having or not having this ability. At the same time, the appearance of formal operation is the psychological base for the development of students'ability of control variables, which make it possible to control variables based on the schema "all other things being equal". Finally, this paper reflects and concludes from the following aspects: tool using in interview, procedures of interview, interviewees and so on.