Prior research highlights the role of number manipulation activities in fostering the early mathematical development of children. This study (N = 1,491) explored the effect of a bear-themed intervention on enhancing arithmetic abilities in kindergarten students. Utilizing a pre- and post-test design, the study compared the advancements of children receiving the intervention to those in a control group. Our findings show that the intervention facilitated improvements in critical skills, including numerical comparison, arithmetic operations, and recognition of numbers and cardinality (in designation but not in production). Furthermore, children partaking in the intervention during their third year of kindergarten performed better than non-participants on number comparison tasks in a national assessment administered after six months (follow-up 1) and again at one year (follow-up 2), although such benefits were not observed on other tasks (e.g., numerical problems). In follow-up 2, the advantages were particularly observable among schools in low-socioeconomic areas. Although the effects were moderate in size and not consistently present across all measures, the results suggest that the intervention may offer sustainable benefits extending beyond the year of implementation. The study also highlights the significance of interventions in early education for reinforcing essential mathematical competencies, especially in economically disadvantaged areas.