The Johnstone–El‐Banna model of problem solving is based on working‐memory theory as well as on Pascual‐Leone's M‐space theory. The operation and validity of the model depends on a number of necessary conditions, such as a simple logical structure, availability and accessibility of the partial steps, absence of “noise,” and lack of familiarity with the problem type. If these, and some other conditions, are not fulfilled, the model may not operate; that is, solvers may be successful, even if the information‐processing demand (Z‐demand) is greater than their information‐processing capacity and, vice versa. Sixteen organic chemical‐synthesis problems, with a simple logical structure and varying Z‐demand from 2 to 8, were used in this work. We studied two samples of students (age 17–18), one without (N = 128) and the other with (N = 191) some previous training (at least in part) in organic‐synthesis problems. Although the predicted pattern was observed in both samples, it was found that the model was more useful in the case of the students without previous training. Finally, the model predicts better with the field‐independent and the field‐intermediate students, but less so with the field‐dependent ones. © 2000 John Wiley & Sons, Inc. Sci Ed 84:131–153, 2000.

ABSTRACT:The Johnstone-El-Banna model of problem solving is based on workingmemory theory as well as on Pascual-Leone's M-space theory. The operation and validity of the model depends on a number of necessary conditions, such as a simple logical structure, availability and accessibility of the partial steps, absence of "noise," and lack of familiarity with the problem type. If these, and some other conditions, are not fulfilled, the model may not operate; that is, solvers may be successful, even if the informationprocessing demand (Z-demand) is greater than their information-processing capacity and, vice versa. Sixteen organic chemical-synthesis problems, with a simple logical structure and varying Z-demand from 2 to 8, were used in this work. We studied two samples of students (age 17-18), one without (N ϭ 128) and the other with (N ϭ 191) some previous training (at least in part) in organic-synthesis problems. Although the predicted pattern was observed in both samples, it was found that the model was more useful in the case of the students without previous training. Finally, the model predicts better with the fieldindependent and the field-intermediate students, but less so with the field-dependent ones.

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The present studies explored the relation between students' achievement in chemistry problem-solving and the Mobility-Fixity dimension. Fixity characterizes consistency of function of field-independent subjects in a field-independent fashion, while Mobility provides for variation according to circumstances. The effect of this cognitive variable was examined as a function of the type and the complexity of the problem. Two kinds of problems were used, chemical equilibrium problems with varying mental demand and logical structure, and organic synthesis problems with varying mental demand. The subjects had to carry out different mental tasks, such as manipulation of logical schemata, applying algorithmic procedures, solving nonalgorithmic problems. In all cases, Mobile subjects demonstrated higher achievement than Fixed subjects. The results of this study support the hypothesis that the Mobility-Fixity dimension can serve as a predictor variable of students' performance on chemistry problem-solving.

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