A detailed experimental study on different processes of heating and cooling allows to deduce that temperature variation, in these processes, in the course of time is not always the same, but it depends, to a great extent, on how the process is carried out. So to confuse the T-Q relations (always lineal) wirth T-t relations (dependent on the process) is a mistake that is necessary to avoid in our classes.

There are some ill ways of designating concepts and processes, in both the textbooks and the language we, teachers of Physics and Chemistry, commonly use in our lessons. This is an obstacle to attain our aims. Furthermore, we do not usually take into account in our educational practice, the alternative frameworks our students have, which makes our ((teaching productivity» alarmingly low in the scientific field. Such situation is analysed in this report, and some suggestions for classroom practice and science teaching are offered.

This paper contributes to clarify concepts such as those of previous knowledge, alternative frameworks and conceptual change, usually conveying very different meanings.La bibliografía sobre la materia es tanta en los últimos tiempos que parecería inútil explicar ahora los conceptos de Idea Previa, Esquema Alternativo y Cambio Conceptual, pero lo haremos, no obstante, porque uno de los motivos del presente trabajo es contribuir a la clarificación de tales conceptos, convencidos como estamos de que se utilizan con sentidos y significados que llegan a ser muy distintos.