Working memory performance affects children’s learning. This study examined objective, subjective, and physiological cognitive load while children completed a spatial working memory complex span task. Frist, 80 Taiwanese 11-year-olds who participated in Experiment 1 confirmed the suitability of the materials. Then, 72 Taiwanese 11-year-olds were assigned to high and low complexity groups to participate in Experiment 2 to test the study hypothesis. Children had to recall at the end of a dual-task list and answer two questions regarding the difficulty and (...) mental effort involved in processing and storage. Their pupil diameters were recorded using an eye-tracker. Two-way mixed ANOVA found that the processing requirements and memory load reduced storage and aggravated the subjective CL of storage; the subjective CL of processing was higher under highly complex conditions. Stepwise regression analysis indicated that subjective CL of processing predicted memory performance in low CL conditions, and physiological CL of processing predicted it in high CL conditions. (shrink)