Purpose - This study explores variation theory-based interventions' contribution to enhancing preschoolers' subitizing abilities during iterative lessons. Results are presented according to low, middle and high achievers, focused on those with prominent challenges. Design/methodology/approach - In total 68 Swedish preschoolers participated. They were randomly assigned to one of the intervention/control groups: 23 mixed design, 24 variation theory design and 21 controls. Data from 59 pupils were analyzed. A learning study with three lesson designs for each intervention group was used in autumn 2022 and spring 2023, respectively. The mixed design met ordinary textbook material and variation theory (VT) group instructions designed by VT during autumn, whereas all met instructions designed by VT in spring. Each group was divided into two subgroups. The controls followed business-as- usual math teaching. Two tests assessed pupils' results before and after the interventions. Findings - All groups showed significant improvements between pre- and post-tests. Pupils in the mixed and VT groups developed more knowledge than the controls. The low-achieving group developed the most. The VT group exhibited a more complex pattern of variation and a greater increase than the mixed group. The intervention groups showed a greater improvement in both tests' results than the controls. Originality/value - There is agreement on the importance of subitizing abilities as a predictor of future mathematical development; however, lesson design and research on pupils' development regarding lessons offered are limited.