A retrospective, school-based, within-class quasi-experimental evaluation of a rhythm-coordination rope-skipping programme and 1-min rope-skipping performance in primary school children.

One-minute rope skipping is a task-specific school performance measure influenced by physical capacity, temporal coordination, rhythm, and task familiarity; whether reorganising routine practice around rhythm- and coordination-oriented, constraint-led tasks yields additional improvement remains unclear. This retrospective, school-based, within-class, non-randomised quasi-experimental evaluation used routine records from one primary school in the Tianfu New Area, Sichuan, China, to examine whether an 8-week rhythm-coordination rope-skipping programme was associated with additional improvement in task-specific 1-min rope-skipping performance relative to usual practice. The analysis included 1,156 children nested within 30 home classes across Grades 2-6; each class had been divided non-randomly into two approximately balanced instructional subgroups using the existing roster and routine timetabling arrangements, so both conditions were represented in every class. The intervention was scheduled three times per week in 30-min sessions over 8 weeks (24 planned sessions), while the comparator continued routine physical education and usual rope-skipping practice. The primary analysis used ANCOVA with baseline adjustment, home-class fixed effects, and small-sample-corrected (CR2) standard errors clustered by class, with Satterthwaite degrees of freedom; sensitivity analyses included class random-intercept, change-score, class-level, wild-cluster-bootstrap, and leave-one-class-out specifications. Groups were comparable at baseline (all standardised differences ≤ 0.05). Mean performance increased from 120.4 to 128.8 skips in the intervention group and from 118.5 to 121.9 skips in the comparator group. In the primary class-adjusted analysis, the intervention was associated with an additional difference of 6.36 skips (95% CI 3.51 to 9.21;