This study investigated the effects of serial position and temporal distinctiveness on serial recall of simple visual stimuli. Participants observed lists of five colors presented at varying, unpredictably ordered interitem intervals, and their task was to reproduce the colors in their order of presentation by selecting colors on a continuous-response scale. To control for the possibility of verbal labeling, articulatory suppression was required in one of two experimental sessions. The predictions were derived through simulation from two computational models of serial recall: SIMPLE represents the class of temporal-distinctiveness models, whereas SOB-CS represents event-based models. According to temporal-distinctiveness models, items that are temporally isolated within a list are recalled more accurately than items that are temporally crowded. In contrast, event-based models assume that the time intervals between items do not affect recall performance per se, although free time following an item can improve memory for that item because of extended time for the encoding. The experimental and the simulated data were fit to an interference measurement model to measure the tendency to confuse items with other items nearby on the list-the locality constraint-in people as well as in the models. The continuous-reproduction performance showed a pronounced primacy effect with no recency, as well as some evidence for transpositions obeying the locality constraint. Though not entirely conclusive, this evidence favors event-based models over a role for temporal distinctiveness. There was also a strong detrimental effect of articulatory suppression, suggesting that verbal codes can be used to support serial-order memory of simple visual stimuli.

Prior research has identified age 9–11 as a critical period for the development of the control-of-variables strategy (CVS). We examine the stability of interindividual differences in children's CVS skills with regard to their precursor skills during this critical developmental period. To this end, we relate two precursor skills of CVS at age 9 to four skills constituting fully developed CVS more than 2 years later, controlling for children's more general cognitive development. Note that N = 170 second- to fourth-graders worked on multiple choice-assessments of their understanding of indeterminacy of evidence and of confounding. We find relations between these two precursor skills and children's CVS skills 2 years later at age 11 in planning, identifying, and interpreting controlled experiments, and in recognizing the inconclusiveness of confounded comparisons (understanding). In accordance with the perspective that both indeterminacy and confounding constitute critical, related yet distinct elements of CVS, both precursor skills contribute to the prediction of later CVS. Together, the two precursor skills can explain 39% of students' later CVS mastery. Overall, the understanding of indeterminacy is a stronger predictor of fully developed CVS than that of confounding. The understanding of confounding, however, is a better predictor of the more difficult CVS sub-skills of understanding the inconclusiveness of confounded comparisons, and of planning a correctly controlled experiment. Importantly, both precursor skills maintain interactive predictive strength when controlling for children's general cognitive abilities and reading comprehension, showing that the developmental dynamics of CVS and its precursor skills cannot be fully ascribed to general cognitive development. We discuss implications of these findings for theories about the development of CVS and broader scientific reasoning.

Building on rich training literature, we examined which skills constituting the control-of-variables strategy (CVS) benefit from a comprehensive training, and which develop similarly during content-focused inquiry at ages 10-12. In addition, we examined whether prior knowledge, reasoning abilities, and reading comprehension explain variation in intervention effects. In a within-classroom, controlled field-experiment, half of N = 618 children from schools located in the German-speaking part of Switzerland were randomly assigned to a training on the CVS, and the other half to an active control group engaging in content-focused inquiry. Mixed-effects models revealed that the CVS training improved children's skills in planning controlled experiments and understanding the indeterminacy of confounded experiments, whereas it did not show specific effects on children's skills in identifying and interpreting controlled experiments. Children with better reasoning abilities and reading comprehension showed the strongest intervention effects on the more difficult skills. The general and differential effects of training remained mostly stable after a period of 6 months. More basic CVS skills seem to develop without targeted training, whereas more advanced ones benefit most from training that meets learners' preconditions. Educational Impact and Implications StatementChildren's understanding of more difficult aspects of controlled experimentation benefits from training, particularly for those with better reasoning abilities and reading comprehension. These findings encourage teaching more advanced aspects of experimentation already in elementary school, which can have visible developmental impact on children's understanding. Classroom-based trainings should consider heterogeneity in children's cognitive abilities and be designed such that all children's understanding benefits, for example, through providing sufficient guidance and support through structured activities that induce cognitive activation.

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