1The operational definition of TOT used throughout the study was retrieval failure for the duration of a 2 Dynamic assessment can be regarded as the determination of 'the zone of proximal development'(Vygotsky,1978). 3 Flexibility in this study is defined as the use of a different approach with different problems or problem types in order to raise computational efficiency. Exercise 1 Exercise 1 1 The operational definition of TOT used throughout the study was retrieval failure for the duration of a 2 Dynamic assessment can be regarded as the determination of 'the zone of proximal development' (Vygotsky, 1978). 3 Flexibility in this study is defined as the use of a different approach with different problems or problem types in order to raise computational efficiency