This study is a qualitative case study that analyzes how 11th-grade high school students explore the concepts of differentiation—average rate of change, instantaneous rate of change, derivative at a point, and derivative function—by integrating sp...
This study is a qualitative case study that analyzes how 11th-grade high school students explore the concepts of differentiation—average rate of change, instantaneous rate of change, derivative at a point, and derivative function—by integrating speech, dragging, and gesture within a touchscreen-based digital tool environment, from the perspective of the Commognition theory. Although differentiation fundamentally involves understanding the local behavior of continuous change and the notion of limits, it is often reduced in school contexts to procedural techniques for calculating slopes. Such procedure-oriented instruction often leads students to treat differentiation not as a conceptual object with relational meaning, but merely as a rule to be applied mechanically when solving problems. Accordingly, this study aimed to investigate how multimodal interactions within a touchscreen-based GeoGebra environment organize and transform students’ mathematical discourse.
The study was conducted with ten 11th-grade students at a public high school in I City. Students worked in five pairs and participated in four 100-minute class sessions held in July 2025(July 9, 11, 16, and 18). Each group used a tablet device and the GeoGebra environment to carry out the exploratory tasks. Data were collected from screen recordings, audio recordings, and dual-camera classroom video. For the analysis, episodes in which speech, gesture, and dragging were integrated were selected and transcribed. Word use, the functions of visual mediators, the reorganization of narratives, routine shifts, and discursive transitions were systematically traced based on the Commognitive analytic framework. Ethical approval and informed consent from both students and guardians were obtained prior to the study.
The exploratory tasks were designed according to a historical–genetic progression. Students first explored tangent lines and then visually examined average rates of change. Through the process of moving one point closer to another, they repeatedly observed how the slope of a secant line approaches the slope of a tangent line. Subsequently, the derivative at a point was formalized, and the tasks were designed so that students could explore the process by which the tangent slope is organized as a function according to changes in the point’s position, leading to the exploration of the derivative function.
The results showed that in Activity 2.1, students observed changes in the average rate of change by manipulating the slider and points, and initially remained within ritualized routines focused on reading values and sharing observations. However, as pauses and deictic actions at specific positions were repeated, students began to produce process-oriented descriptions of slope, such as “it keeps increasing” and “it is not constant”. In Activity 2.2, as students continuously dragged one point to reduce the distance between the two points, they produced absence-deictic narratives such as “the slope suddenly disappears” and “if the two points completely overlap, we cannot talk about the slope.” Soon afterward, a definition-adjacent condition such as “B does not become A but only gets closer” was constructed. This episode represents a case in which a shift from ritualized routines to exploratory routines was observed. In Activity 3, a representational linkage was provided in which, as point A moves, the slope of the tangent corresponds to the coordinate of point B, and the locus of point B appears as a single curve. Through this linkage, students began to name slope not as an isolated numerical value but as a new functional object that “that takes values that vary with .” In other words, the tangent slope was no longer treated as merely the result of a calculation, but was handled in discourse as a functional object organized according to the position of the point. In Task 4, students moved point A along the original function and examined the tangent slope at each . They manipulated red point corresponding to the coordinate and repeatedly verified, through the locus and checkbox functions, how a set of points becomes organized into a single graph. During this process, chained discursive shifts were observed in which slope was reorganized from a local computed value into an object with a functional structure, as evidenced by utterances such as “Oh? This is the same as the tangent slope,” and “Then isn’t the tangent slope a quadratic function?” Subsequently, the derivative function began to be referred to as a criterion for judging the increase and decrease of the original function. In the touchscreen environment, continuous dragging functioned as a dynamic visual mediator that accomplished the sharing of change, while the pause of dragging functioned as a static visual mediator that established joint attention. In addition, finger-based manipulation facilitated the repetition of “pause–check–re-drag,” thereby supporting the stabilization of exploratory routines and discursive shifts.
In the core exploratory episodes of this study, it was confirmed that students participated in discourses of comparison, observation, interpretation, and justification through interactions in which static and dynamic visual mediators intersected. This study is significant in that it demonstrates, through concrete cases, that a digital tool can reorganize discourse related to differentiation from a procedure -centered orientation toward a relation- and justification-centered orientation by mediating representational synchronization and repeated verification.