Aims: Children with neuromotor delays are at risk for reaching and object exploration impairments, which may negatively affect their cognitive development and daily activity performance. This study evaluated the effectiveness of the Sitting Together And Reaching To Play (START-Play) intervention on reaching-related exploratory behaviors in children with neuromotor delays. Methods: In this randomized controlled clinical trial, 112 children (Mean=10.80, SD=2.59 months old at baseline) with motor delays were randomly assigned to receive START-Play intervention or usual care-early intervention. Performance for ten reaching-related exploratory behaviors was assessed at baseline and 1.5, 3, 6, 12 months post-baseline. Piecewise linear mixed-effects modeling was used to evaluate short- and long-term effects of the intervention. Results: Benefits of START-Play were observed for children with significant motor delays, but not for those with mild delays. START-Play was especially beneficial for children with significant motor delays who demonstrated early mastery in the reaching assessment (i.e., object contact 65% of the time within 3 months after baseline); these children showed greater improvements in manual, visual, and multimodal exploration, as well as intensity of exploration across time. Conclusions: START-Play advanced the performance of reaching-related exploratory behaviors in children with significant motor delays. [This paper is the online first version of an article published in "Physical & Occupational Therapy in Pediatrics."]