Teaching and Teacher Education 15 (1999) 653}665 The decimal point situation: a close look at the use of mathematics-classroom-situations in teacher education Zvia Markovits*, Ruhama Even Center for Mathematics Education, Oranim School of Education, Tivon, 36006, Israel Department of Science Teaching, Weizmann Institute of Science, Rehovot, 76100, Israel Received 21 April 1998; received in revised form 16 November 1998; accepted 27 January 1999 Abstract Mathematics classroom situations (MCS) are real or hypothetical classroom situations involving mathematics, in which the teacher has to respond to a student's hypothesis, question or idea. This study investigates the use of one such situation, the decimal point situation, in an in-service course for 20 elementary teachers. Data sources include: written questionnaire, individual interview, whole class discussion and student interview. The article examines the potential of MCS to evoke analyses and re#ections about teaching and learning mathematics.  1999 Published by Elsevier Science Ltd. All rights reserved. 1. Introduction Teaching has come to be recognized as a com- plex and ill-structured domain where theory cannot instantly determine action, i.e., `correct answersa cannot be derived through direct application of appropriate principles and theories (e.g., Merseth, 1996; Shulman, 1992, 1986). In many cases, teacher action derives from and builds on contex- tual and local situations and experiences. Conse- quently, teacher educators and sta! developers have lately begun to develop and use a variety of materials that focus on speci"c problematic situ- ations as a means to evoke thoughtful analyses and re#ection about teaching and learning mathematics * Corresponding author. Tel.: #972-4-9838850; fax: #972- 4-9838761. E-mail address: zviam@mofet.macam98.ac.il (Z. Markovits)  Tel.: #972-8-9343157; fax: #972-8-9344115 (e.g., Barnett, Goldenstein & Jackson, 1994; Hirshfeld, Robinson, Radai & Even, 1996; Wilcox & Lanier, in press). Our work in the last years belongs to the same trend. We prepare descriptions of real or hypotheti- cal classroom situations involving mathematics, in which the teacher has to respond to a student's hypothesis, question or idea. The situations we designed for junior-high school teachers center on the mathematical function concept; those aiming at elementary school teachers focus on arithmetic and number sense. All deal with students' ways of think- ing and with various characteristics of teachers' responses to students. These mathematical class- room situations (MCS) are similar to `casesa in that they focus on speci"c problematic teaching situations (for a comprehensive review of the use of cases in teacher education, see Merseth, 1996). However, MCS may be hypothetical (although they are based on real events or research), and they 0742-051X/99/$ - see front matter  1999 Published by Elsevier Science Ltd. All rights reserved. PII: S 0 7 4 2 - 0 5 1 X ( 9 9 ) 0 0 0 2 0 - 7