Although there is growing interest in studies of teachers' actions and conceptions, little is known about content-related teaching problems arising in science classrooms. This article presents a case study of problems which can occur when teaching the topic of redox reactions to Grade 11 students. Two chemistry teachers, a senior and a junior teacher, were involved in the study. Their reflective comments on the teaching problems were also investigated. Research data were obtained from classroom observations and audiotaped recordings of classroom practice. After the lessons, we conducted semistructured interviews with the teachers. The teaching problems are reported in terms of teaching activities causing difficulties for students in considering new conceptions to be necessary, intelligible, plausible, or fruitful. Analyses of the teachers' comments on these teaching activities clarifies a number of reasons why they acted as they did. It can be concluded that teachers' scientific expertise is an important source of difficulties when teaching redox reactions. Implications for an improvement of current chemistry classroom practice and contentrelated teacher training are offered.

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This article addresses ideas about the particulate nature of matter that are considered to be correct or acceptable in science education and studies of children's misconceptions. It argues that science teachers and educators use educational as well as scientific criteria for correctness, and that these criteria do not always coincide. Relations between the particulate nature of matter in science and science education are analyzed in an attempt to make more intelligible children's inclination to attribute all kinds of macroscopic properties to particles.

Teaching the chemical reaction concept to young students requires a more disciplined way of using substance names, as well as other strategies.

Much attention has been paid to guided discovery as a teaching method, however, teachers have been given little concrete advice on how to carry this out. In this paper, we attempt to guide "the guide" on a new road to the concept of chemical reactions. Communicating the BasicsEducation in chemistry begins relatively late in Holland: students are 14 or 15 when they first see a chemistry teacher teach. These students, probably just like those in other countries, have great difficulty in grasping and understanding the concept of "chemical reaction." Failure at this basic level usually means a frustrating experience for the student and teacher alike. The program to be described herein involves a conscience effort to address and solve this problem.In learning chemistry, we feel, students should be encouraged to discuss chemical phenomena among themselves using their own terminology. The teacher should create situations in which students discover deficiencies in their own vocabulary when trying to communicate their observations and ideas. A new meaning of a word such as "reaction" is not understood by just listening to a teacher using or even defining the word.

Some of the major problems in teaching and learning chemistry are encountered in the very first stages of an elementary chemistry course. This seems to be a paradox since obviously one aims at teaching the simplest things first, but in fact it is not.The knowledge gap between teacher and student is at its widest when the student is relatively young and knows next to nothing about chemistry. The teacher, trained as a chemist, has adopted concepts, facts, models, rules, and theories that, govern his or her thoughts and perception. It is difficult for the teacher to cast aside this structure even for the purpose of understanding a beginner's learning problems.

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A PhD research project to explicate a conceptual structure of chemistry curricula.