This research reports the implementation of an evaluation instrument of the slope concept in high school students. The design of this study was based on four dimensions: Skills, Properties, Uses and Representations (SPUR model; Thompson & Kaur, 2011) and on three conceptualizations: constant ratio, behavior indicator and trigonometric conception. This work adopts a qualitative approach to analyze the students' productions and a quantitative approach when obtaining the percentages of the student's responses. The general objective of the work is to evaluate the effect produced by a group of tasks designed with the SPUR model on the slope concept in high school students. The results show that students have traditional conceptualizations of the slope as a constant ratio and trigonometric conception. However, these conceptualizations emphasize more procedural aspects than conceptual ones. This finding could partially explain why students can solve certain tasks of procedural nature but not conceptual tasks that usually require a multifaceted view of the slope.