The present study used data from the Trends in International Mathematics and Science Study (TIMSS) 2003 to look at the trend in instructional strategies in science teaching and its effect on the science achievement. Based on the analysis, the strategies used by most science teachers were demonstration, practical work and the lecture method. Among these strategies, the most commonly used in Malaysia was the lecture method where more than 90% of the teachers involved in TIMSS used this strategy. Students in classes where their teachers demonstrated experiments, where students perform experiments and also where students listened to lectures performed significantly higher in the TIMSS science achievement. It was also found that students were more likely to give explanations to their observations than to design their own experiments. These findings suggest that ample opportunities should be given for students to design their experiments which include formulating hypotheses, making predictions and giving explanations to the outcomes of their experiments. (Contains 3 tables.)