Several decades of research and development have produced a rich ecology of technologies designed to support active, collaborative constructionist pedagogical practices. Nevertheless, many teachers are reluctant to use these technologies in their teaching or fail to devise learning designs which leverage their qualities. We argue that this tension reflects a dissonance between the epistemic practices (manners of constructing knowledge) implicit in teachers' pedagogical practices and the ones embodied in the technology. We demonstrate this argument in the case of Dynamic Mathematics Environments (DME) through the epistemic practice of identifying invariants, and its dynamic manifestation in the technology, and illustrate it further with examples from an online course on CSCL. For teachers to effectively design learning experiences in a technology rich environment, they need to develop their capacity to critically assess the epistemic and pedagogical practices associated with this environment, identify a set of target epistemic practices and carefully devise the pedagogical practices which will engender these. We call these "generative pedagogical practices." To do so, teachers need to actively participate in activities that would provide them with opportunities to make that epistemic change: building, experimenting with and designing for learning in diverse environments. Sometimes, applying such an epistemic disposition, requires suppressing old practices of activity design.