Short-term memory development: Differences in serial position curves between age groups and latent classes Gabriela V. Koppenol-Gonzalez a,⇑ , Samantha Bouwmeester b , Jeroen K. Vermunt a a Department of Methodology and Statistics, Tilburg University, NL-5000 LE Tilburg, The Netherlands b Department of Psychology, Erasmus University Rotterdam, NL-3000 DR Rotterdam, The Netherlands article info Article history: Received 11 September 2013 Revised 11 April 2014 Keywords: Cognitive development Short-term memory Methodology Latent class analysis Individual differences Similarity effect abstract In studies on the development of cognitive processes, children are often grouped based on their ages before analyzing the data. After the analysis, the differences between age groups are interpreted as developmental differences. We argue that this approach is prob- lematic because the variance in cognitive performance within an age group is considered to be measurement error. However, if a part of this variance is systematic, it can provide very useful information about the cognitive processes used by some children of a certain age but not others. In the current study, we presented 210 children aged 5 to 12 years with serial order short-term memory tasks. First we analyze our data according to the approach using age groups, and then we apply latent class analysis to form latent classes of children based on their performance instead of their ages. We display the results of the age groups and the latent classes in terms of serial position curves, and we discuss the differences in results. Our find- ings show that there are considerable differences in performance between the age groups and the latent classes. We interpret our findings as indicating that the latent class analysis yielded a much more meaningful way of grouping children in terms of cognitive processes than the a priori grouping of children based on their ages. Ó 2014 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.jecp.2014.04.002 0022-0965/Ó 2014 Elsevier Inc. All rights reserved. ⇑ Corresponding author. Address: Department of Pedagogical and Educational Sciences, Erasmus University Rotterdam, NL-3000 DR Rotterdam, The Netherlands. E-mail address: koppenolgonzalez@fsw.eur.nl (G.V. Koppenol-Gonzalez). Journal of Experimental Child Psychology 126 (2014) 138–151 Contents lists available at ScienceDirect Journal of Experimental Child Psychology journal homepage: www.elsevier.com/locate/jecp