Abstract
<jats:p xml:lang="en">The aim of this study is to reveal external visual representations of pre-service mathematics teachers towards number sets, to identify reasons for errors in representations and to create a lesson plan that can overcome the errors. In this context, the study is an example of action research. The first stage of the study was devoted to revealing external visual representations of pre-service mathematics teachers. The second stage of the study was devoted to lesson plan that can overcome the existing errors obtained in the first stage. Error-based activities with argumentation-based learning was determined as teaching method in the lesson plan. As a result of the study, 30 different errors were determined in their external visual representations. It was determined that the lesson plan was effective in overcoming the errors in external representations and in creating appropriate internal representations.</jats:p>