Concurrent and Construct Validity of the Diagnoform® Kid Physical Fitness Test Battery in Primary School Children

Background: Physical Fitness (PF) is an important health marker that should be regularly monitored with simple, time-efficient test batteries such as Diagnoform® Kid. However, its validity remains insufficiently evaluated. Therefore, this cross-sectional study examined its concurrent and construct validity against a battery of established reference tests. Methods: 184 children were grouped by age (6–7, 8–9 and 10–11 years). The Diagnoform® and reference batteries assessed identical PF components using the following tests: 6-min shuttle run-walk vs. reduced Cooper for cardiorespiratory fitness, hopscotch vs. quadrant jump for agility, standing broad jump with vs. without execution instructions for power, 5-s sprint vs. 20-m sprint for speed, and simplified fingertip-to-floor vs. sit-and-reach for flexibility. Concurrent validity was examined using bivariate correlations, and construct validity through responsiveness to age and sex. Results: Corresponding tests were significantly correlated for all PF components (p < 0.001), except for agility at 10–11 years (p = 0.094). Agility showed moderate correlations in the younger groups (r = −0.45 to −0.67). Correlations were strong for cardiorespiratory fitness and flexibility (r ≥ 0.70). For power and speed, correlations ranged from moderate (power: r ≥ 0.61 at 6–7 and 8–9 years; speed: r = 0.58 at 6–7 years) to strong (power: r ≥ 0.83 at 10–11 years; speed: r ≥ 0.70 at 8–9 and 10–11 years). Age and sex influenced performances in both batteries, except for agility (no sex effect observed) and flexibility (sex effect observed in both batteries, whereas an age effect was found only for boys on the reference test). Conclusions: Despite slightly lower responsiveness of the simplified fingertip-to-floor test to age, findings support the concurrent and construct validity of the Diagnoform® Kid tests.