High school and college students often carry out of traditional physics courses loose bundles of vague and undifferentiated concepts about physical objects and their properties. Within the framework of schematic modeling, a scientific concept can be defined explicitly with five schematic dimensions: domain, organization, quantification, expression, and employment. Based on the level of commensurability between scientific concepts and individual students' own concepts, students' cognitive evolution into the scientific realm can take different directions ranging from reinforcing existing concepts to constructing novel ones on completely new foundations. Such evolution is promoted in a student-centered, model-based instruction. The newtonian concept of force is discussed for illustration, along with the results of tutoring two groups of Lebanese students to develop this concept in a schematic modeling approach.