Cognitive load can be assessed and monitored using a multitude of subjective (self-reports, i.e. Hart & Staveland, 1988; Paas, 1992) and more objective methods (dual tasks, eye-tracking, heart-rate measurements, skin conductance measurements, cf. Brünken, Plass, & Leutner, 2003; Beatty, 1982, Paas, van Merriënboer, & Adam, 1994), either during the learning or afterwards, so that instruction can be optimized based on mental effort data using iterative design (a cyclic process of prototyping, testing, analyzing, and refining a product or process, ultimately improving the quality and functionality of the design). Computer simulations provide an excellent environment to apply CLT principles. However, such e-environments are technically complex and therefore add to extraneous load. Separating the technical knowledge of how to use the computer interface from the actual conceptual knowledge using sequencing should reduce this load to a reasonable extent (cf. Clarke, Ayres & Sweller, 2006). The authors provide guidelines on how to use CLT in the design of e-environments and discuss what future directions can be taken to further optimize the design of such environments.