The traditional model of knowledge acquisition is one of accumulation of discrete units of information that have been assimilated and are stored in memory. Modern cognitive research suggests a different, more accurate model, called conceptual change. Children (and adults) bring an existing set of understandings to any new learning. These understandings shape the ways in which new material is assimilated and may themselves undergo change. Knowledge acquisition, then, is new understanding that occurs when existing understandings come into contact with new evidence and are modified as a result. Rather than an accumulation of facts.