Introduction Fine motor development in preschool-aged children requires appropriate and ongoing stimulation. This study aimed to examine differences in changes in fine motor development between preschool-aged children receiving the Hand-In-Hand Book intervention and those receiving routine school activities. Methods A quasi-experimental pretest-posttest control group design was employed involving 44 children aged 48–66 months from RA BA Aisyiyah Mlideg and TK Dharma Wanita Ngrandu, Bojonegoro Regency, with 22 children in each group. Total sampling was used, with group allocation conducted at the school level and one school representing each group. The intervention consisted of the Hand-In-Hand Book, a busy book combined with cooperative play, administered over 2 weeks in 10 sessions of 30 minutes each. Fine motor development was assessed using a researcher-developed observation sheet based on age-appropriate KPSP indicators. The primary outcome was the change in fine motor scores from pretest to posttest. Data were analyzed using the Mann–Whitney U test. Results The proportion of children meeting the expected fine motor criteria in the intervention group increased from 18.2% at pretest to 100% at posttest, while no change was observed in the control group. A statistically significant difference in score changes was observed between groups (U = 44.00, Z = −5.416, p < 0.001), with a large effect size (r = 0.82). Discussion and Conclusion However, because school site was completely confounded with intervention, the observed difference cannot be attributed solely to the intervention. Further studies using multiple schools and more rigorous allocation procedures are needed.