The best indicator for assessing a child's growth status is biologic/developmental age because it reflects the child's physiological and maturational stage rather than just the passage of time. Chronological age may not correspond to actual growth and maturation due to individual variability. Developmental age incorporates the assessment of skeletal, sexual, and cognitive maturity, providing a more accurate evaluation of growth potential and health status. This approach is crucial for identifying growth disorders and planning appropriate interventions.

Reference: Nelson Textbook of Pediatrics, Kliegman et al., 21st Edition.