Abstract
The purpose of this paper is to report the analysis of senior secondary students' proof using
deduction on an exercise based on a parallelogram. The question was designed so that it could be
solved by recourse to a relatively little used definition of a parallelogram. The results showed
that the better students did make use of the definition. However, the majority of students who
chose to use a deductive approach, relied initially on congruency concepts. For these responses a
clear difference in quality was identified. Because of this work a general framework of growth,
based on the SOLO Taxonomy, is suggested. Following from this a possible structure of the
nature of early Level 4 (deductive) thinking identified by the van Hiele theory is hypothesised.
John Pegg & Susan Woolley
AN INVESTIGATION OF STRATEGIES USED TO SOLVE A SIMPLE DEDUCTIVE EXERCISE IN GEOMETRY