Recent developments in concept learning and in science-for-all curricula have stimulated our interest in two fields of study: how students move between their everyday life-world and the world of school science, and how students deal with cognitive conflicts between those two worlds. In the first field of study, Aikenhead conceptualized the transition between a student's life-world and school science as a cultural border crossing. In the second field, Jegede explained cognitive conflicts arising from cultural differences between students' life-world and school science in terms of collateral learning. This article (a) synthesizes cultural border crossing with its cognitive explanation (collateral learning) and (b) demonstrates by its example the efficacy of reanalyzing interpretive data published in other articles. The synthesis provides new intellectual tools with which to understand science for all in 21st-century science classrooms in developing and industrialized countries. © 1999 John Wiley & Sons, Inc. J Res Sci Teach 36: 269–287, 1999