This study evaluated the short-term effectiveness of a multidisciplinary residential obesity treatment program by describing changes in body weight, related measures, and gross motor co-ordination. Secondarily, it was examined to what extent the amount of relative weight loss achieved by overweight and obese (OW/OB) participants explained the projected improvement in gross motor co-ordination. Thirty-six OW/OB children (aged 10.5 ± 1.4 years, 12 girls and 24 boys) were recruited at the Zeepreventorium VZW (De Haan, Belgium), where they followed a specific program consisting of moderate dietary restriction, psychological support, and physical activity. For reference purposes, an additional group of 36 age- and gender-matched healthy-weight (HW) children was included in the study. Anthropometric measures were recorded and gross motor co-ordination was assessed using the Körperkoordinationstest für Kinder (KTK) on two occasions with an interval of 4 months. Regardless of the test moment, OW/OB participants displayed significantly poorer KTK performances (P < 0.001). However, treatment was found to be efficacious in decreasing body weight (Δ 17.9 ± 3.1%, P < 0.001) and generating a significant progress in gross motor co-ordination performance, with a greater increase in KTK score(s) from baseline to re-test as compared to HW peers (P < 0.01). Within the OW/OB group, the amount of relative weight loss explained 26.9% of the variance in improvement in overall KTK performance. Therefore, multidisciplinary residential treatment and concomitant weight loss can be considered an important means to upgrade OW/OB children's level of gross motor co-ordination, which in turn may promote physical activity participation.