RUNNING HEAD: MAGICAL NUMBER FOUR IN MENTAL ROTATION The Magical Number Four in Children’s Mental Rotation of Cube Aggregates Nikolay Lütke Christiane Lange-Küttner London Metropolitan University, London, UK Accepted 6 th November 2020 © 2020, American Psychological Association. This paper is not the copy of record and may not exactly replicate the final, authoritative version of the article. Please do not copy or cite without authors' permission. The final article will be available, upon publication, via its DOI: 10.1037/dev0001139 Please cite: Lütke, N. & Lange-Küttner, C. (in press). The magical number four in children’s mental rotation of cube aggregates. Developmental Psychology, DOI: https://doi.org/10.1037/dev0001139 Author Note The study is part of the first author’s PhD research on mental rotation test development for children, awarded in October 2020. The second author currently works at the University of Bremen, Germany. Correspondence concerning this article should be addressed to Christiane Lange-Küttner, Dept. of Psychology, University of Bremen, P. O. Box 330 440, 28334 Bremen, Germany, email ch_la4@uni-bremen.de.