Multisport vs. Single-Sport Training and Motor Coordination in Children: A Quasi-Experimental Pre–Post Comparison

Background: This study aimed to compare changes in motor coordination associated with two different motor practice models—multisport and single-sport soccer training—in children, without implying causal effects of one training context over the other. Methods: A quasi-experimental pre–post study (T0–T1) was conducted over 10 weeks in non-randomized, pre-existing groups. A total of 143 children (mean age: 6.21 ± 0.55 years; 107 males) were allocated to a Multisport Group (MG; n = 79) and a Single-sport Group (SG; n = 64). Motor coordination was assessed using the Körperkoordinationstest für Kinder (KTK), and raw scores (RAW SCORE) were used for analysis. Statistical analyses included t-tests, change-score (Δ) and effect-size analyses, and two-way repeated-measures ANOVA. Results: Both groups showed significant improvements over time (p < 0.001; d = 0.75 for MG, d = 0.77 for SG). However, the MG showed significantly greater improvements than the SG (Δ = 16.68 ± 6.14 vs. 12.28 ± 4.08; p < 0.001; d = 0.83). At T1, the SG still showed slightly higher absolute RAW SCORE values than the MG (p = 0.049; d = −0.33), although this between-group difference was markedly reduced compared to baseline (d = −0.59). The ANOVA revealed a very large effect of Time (F(1,141) = 1092.31, p < 0.001, η2p = 0.886), a small-to-medium effect of Group (F(1,141) = 7.51, p = 0.007, η2p = 0.051), and a large Time × Group interaction (F(1,141) = 24.18, p < 0.001, η2p = 0.146). A sensitivity analysis (ANCOVA) confirmed that, after adjusting for baseline scores, sex, and anthropometric variables, the Multisport group showed significantly higher adjusted T1 scores than the Single-sport group (adjusted mean difference = 3.96 points, 95% CI: 1.93–5.99), reversing the direction observed in the unadjusted T1 comparison. Given the non-randomized design and baseline group differences, findings reflect observed associations rather than causal effects. Conclusions: Both practice models were associated with improved motor coordination, with multisport participation associated with greater observed change over 10 weeks. These findings are consistent with a possible role of diversified motor experiences in coordination development, though this study cannot establish causality.