Based on a critical re-analysis of cognitive load theory (CLT), Schnotz and Kurschner identified the need for research on more sensitive ways of assessing learner characteristics, both prior to and during instruction, in order to understand learning processes and outcomes. One emergent theme of the papers in this special issue is that the "same" learning environment is differentially demanding and produces different results depending on characteristics of the learners, most importantly their knowledge in the task domain. These findings indicate that to optimize learning outcomes, theories of instructional design and learning need to be more adaptive and reflect the nuances of interactions among learners, tasks, and instructional supports.