Introducing SOLO Theory Focusing on its Application in Geometry

To facilitate the deep learning of mathematics among learners, it is imperative to make an effort to comprehend the developmental conditions and assess their thinking levels. Numerous theories exist that describe the growth and thinking levels of learners. Among these theories, the Structure of the Observed Learning Outcome (SOLO) taxonomy stands out as a highly practical approach. SOLO serves as a valuable instrument for evaluating the quality of individuals' responses when solving problem. The purpose is to describe this theory, focusing on its application in geometry and its importance in the teaching and learning process, and to make a comparison between SOLO theory and van Hiele theory. SOLO taxonomy, based on two characteristics examines the learner's understanding of mathematical concepts. The initial characteristic is related to the various levels of an individual's response or capacity to respond, which are categorized into five distinct levels: pre-structural, uni-structural, multi-structural, relational, and extended abstract. The second characteristic is related to the mode of thinking, whereby it is believed that learning takes place through one of the five modes of thinking: sensory-motor, iconic, concrete symbolic, formal, and post formal. While SOLO theory is applicable to all mathematical subjects, including geometry, there is limited research on its application in the realm of geometry. Most studies instead concentrate on van Hiele's theory when evaluating the various levels of geometric thinking. In this review article, which has been done using a library method, the SOLO and van Hiele theories and their comparison are discussed based on valid studies. The aim is to provide planners and teachers with a new view on the level of geometric thinking. Moreover, it offers valuable insights for reviewing the geometry teaching process and evaluating learners' geometric thinking levels.