Students' conceptions are characterized by some authors as having a high degree of coherence while, in the minds of others, they show little coherence and great heterogeneity. The objective of this study was to throw light on this problem by reference to the particulate nature of matter, a topic where great discrepancies have been observed in the degree of coherence shown by students. We interviewed 43 students aged 9-22 years to evaluate the coherence of their replies, using a questionnaire in which different methodological strategies are incorporated, as will be explained below. A qualitative analysis of the students' replies to the interviewer's questions permitted a group of empirical categories to be established, which were then arranged hierarchically. The quantitative analysis of these categories gave rise to new categories, which we call structural categories. These permitted us to select the most significant variables, to identify the different types of conceptions held by the subjects and to assign to each a given level of conceptualization. They also revealed the high degree of coherence in the replies given to different tasks. The usefulness of the proposed method for studying students' conceptions and for evaluating their degree of coherence is confirmed. ß

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This commentary is a critical appraisal of Gil-Pérez et al.'s (2002) conceptualization of constructivism. It is argued that the following aspects of their presentation are problematic: (a) Although the role of controversy is recognized, the authors implicitly subscribe to a Kuhnian perspective of 'normal' science; (b) Authors fail to recognize the importance of von Glasersfeld's contribution to the understanding of constructivism in science education; (c) The fact that it is not possible to implement digitalcommons.unl.edu

This article addresses the process of designing and validating a questionnaire on the New Water Culture, which aims to collect information on various issues related to water, such as its management, savings, and consumption. The questionnaire was subjected to a double validation process: an evaluation by a panel of experts, including members of the New Water Culture Foundation, and a pilot study, which allowed us to estimate the validation of the content as well as the corresponding internal consistency of the questionnaire. The construction and validation process resulted in a questionnaire consisting of 27 items with a total of 71 variables distributed in four sections: the first is related to scarcity, quantity, and distribution of water; the second collects questions about the different dimensions of water; the third analyses the different ways of carrying out water management; and the fourth and last section is related to personal actions associated with water. The reliability study showed a Cronbach alpha of 0.913, which demonstrates the development of a robust and reliable instrument allowing the identification of the most problematic issues associated with the New Water Culture.

The catalogue of conceptions that students are said to have concerning the different topics of the science curriculum is so great that some authors consider this line of research to be exhausted. However, others insist on the need to re-examine students' conceptions in order to better describe them using new theoretical, contexts and research methods. We present an integrated set of guidelines and methodological techniques for selecting those replies that best reflect students' knowledge.