The present study sought to identify the previous knowledge a group of students possessed about trigonometry so that educational activities could be developed in order to teach, clarify and help students comprehend the related concepts. As an educator, I delved into Ausubel’s and Vergnaud’s theories in an attempt to help my students with conceptual and procedural difficulties to relate trigonometry to real life. Results show that identifying the students’ previous knowledge and making the knowledge-in-action explicit results in a change of attitude both on the part of the student and on the part of the teacher.