Previous studies indicate that many preservice science teachers lack facility with those formal reasoning patterns that are critical for learning science. The purpose of this project was to develop, implement and evaluate a curriculum package directed at improving preservice secondary ~,cience teachers' scientific thinking. A matched treatment-control, quasi-experimental design revealed significant gains achieved through use of the curriculum materials. INTRODUCTION Formal reasoning ability has been found to be an important factor influencing student learning in high school science. Studies in the United States (Cantu & Herron, 1978; Lawson & Renner, 1975; Sayre & Ball, 1975) and Australla (Garnett, Tobin & Swingler, 1985) have indicated that science achievement and the understanding of science concepts are significantly related to students' ability to use formal reasoning patterns. Similarly, Padilla, Okey and Dillashaw (1983) found that facility with science process skills _correlates strongly with formal reasoning ability. These findings provide substantial support for the view (De Career, Gabel & Staver, 1978; Lawson, 1985) that a major goal of science education must be to promote the development of students' formal reasoning abililty. It has been shown that a significant number ofpreservice science teachers lack facility with those formal reasoning patterns that are necessary for working on scientific investigation tasks (Garnett & T obin,1984). Such cognitive limitations are likely to reduce their effectiveness in teaching high school students the scientific thinking skills associated with materials-centred science curricula (robin & Garnet!, 1984). Some researchers have investigated whether students' ability to use formal reasoning skills can be improved by instruction. This research has, for the most part, focused on attempts to teach specific reasoning patterns. In a comprehensive review, Lawson (1985) conduded that such training procedures can be successful and that the degree of success depends on the age of students, the length and diversity of the training experiences and the extent to which students are confronted with thought-provoking situations and placed in control of their own actions. 20 Volume 15, No. 2, 1990 AllstralianJournal a/Teacher Education The aim of this study was to implement and evaluate the effectiveness of an educational intervention designed to teach preservice secondary science teachers those formal reasoning patterns necessary for conducting scientific investigations.