Research into learners’ ideas about science suggests that students often have alternative conceptions about important science concepts. Because of this dissatisfaction, constructivism has been adopted as a theoretical framework by many teachers and researchers, and it has had a curricular influence in many countries. Constructivism is much more than an educational doctrine and we are aware that a ‘science war’ about the possibility of objectivity is in progress. ‘Constructivism’ cannot necessary be a package deal: it must be possible to accept educational suggestions deemed useful without buying all the epistemology or the metaphysical implications. The claim that cognitive agents understand the world by constructing mental representations of it can be a shared suggestion for changing science instruction. Many teachers are much more concerned in finding productive teaching methods than about philosophical questions as if knowledge must be considered an objective representation of the real world or not. We have to ponder if some ideas from the constructivist theory of instruction can help instructors to become better teachers. The pragmatic suggestions that come from the constructivist theory of instruction developed by von Glasersfeld, the leading proponent of radical constructivism, could be a good start in this search.