biostudies-literaturePark YNICHD NIH HHSNational Institutes of Healthe13043https://www.ebi.ac.uk/biostudies/studies/S-EPMC8742982biostudies-literatureUnknown24(3)Humans perceptually extract quantity information from our environments, be it from simple stimuli in isolation, or from relational magnitudes formed by taking ratios of pairs of simple stimuli. Some have proposed that these two types of magnitude are processed by a common system, whereas others have proposed separate systems. To test these competing possibilities, the present study examined the developmental trajectories of simple and relational magnitude discrimination and relations among these abilities for preschoolers (n = 42), 2nd-graders (n = 31), 5th-graders (n = 29), and adults (n = 32). Participants completed simple magnitude and ratio discrimination tasks in four different nonsymbolic formats, using dots, lines, circles, and irregular blobs. All age cohorts accurately discriminatDevelopmental scienceMore than the sum of its parts: Exploring the development of ratio magnitude versus simple magnitude perception.PMC87429821R03HD081087‐01R01 HD088585R03 HD0810871R01HD088585‐01Matthews PGPark YViegut AAfalseMore than the sum of its parts: Exploring the development of ratio magnitude versus simple magnitude perception.Humans perceptually extract quantity information from our environments, be it from simple stimuli in isolation, or from relational magnitudes formed by taking ratios of pairs of simple stimuli. Some have proposed that these two types of magnitude are processed by a common system, whereas others have proposed separate systems. To test these competing possibilities, the present study examined the developmental trajectories of simple and relational magnitude discrimination and relations among these abilities for preschoolers (n = 42), 2nd-graders (n = 31), 5th-graders (n = 29), and adults (n = 32). Participants completed simple magnitude and ratio discrimination tasks in four different nonsymbolic formats, using dots, lines, circles, and irregular blobs. All age cohorts accurately discriminat2021-01-01T00:00:00Z2021 May2025-04-22T09:57:44.705Z2025-04-05T23:22:22.65ZS-EPMC87429823303029110.1111/desc.13043