The two separate projects described have examined how teachers exploit computer-based technologies in supporting learning of science at secondary level. This paper examines how pedagogical approaches associated with these technological tools are adapted to both the cognitive and structuring resources available in the classroom setting. Four teachers participated in the first study, undertaken as part of the InterActive Education project in Bristol; all of them used multimedia simulations in their lessons. The second study presented was part of the wider SET-IT project in Cambridge; 11 teachers in eight schools were observed using multimedia simulations, data logging tools and interactive whiteboards. Teachers were interviewed in all cases to elicit their pedagogical thinking about their classroom use of ICT. The findings suggest that teachers are moving away from only using "real" experiments in their practice. They are exploring the use of technologies to encourage students to engage in "What If" explorations where the outcomes of "virtual" experiments can be immediately accessed, for example through using a simulation. However, this type of activity can serve just as a mechanism for revealing--and indeed reinforcing--students' informal conceptions if cognitive conflict is not generated or remains unresolved. The teachers in our studies used simulations, data logging, projected animations and other dynamic digital resources as tools to encourage and support prediction and to demonstrate scientific concepts and physical processes--thereby "bridging the gap" between scientific and informal knowledge. They also integrated technology carefully with other practical activities so as to support stepwise knowledge building, consolidation and application. Research of this kind has design implications for both curriculum-related activities and emerging computer-based learning technologies, in terms of helping us to understand how teachers capitalise upon the technology available in supporting students to construct links between scientific theory and empirical evidence.