WHO Windows of Achievement for Gross Motor Milestones (WHO-GMM)

Six simple movement milestones, and the natural age ranges in which healthy children around the world reach them — that is the WHO Windows of Achievement.

In short

The WHO Windows of Achievement for Gross Motor Milestones (WHO-GMM) is a research-based reference, published by the World Health Organization, that describes the typical age ranges in which healthy children reach six key gross-motor (big-movement) milestones. It assesses when — not how well — a child sits, stands and walks, by giving a normal window of months for each skill rather than a single fixed deadline. It is a guide for understanding healthy variation, not a diagnostic test.

What the WHO-GMM looks at

The WHO-GMM grew from a large multi-country study that followed healthy, well-nourished children across diverse settings, confirming that early motor development follows a remarkably similar pattern worldwide. It maps six milestones, each with its own age window:

• Sitting without support
• Standing with assistance
• Hands-and-knees crawling
• Walking with assistance
• Standing alone
• Walking alone

The gift of the window idea is reassurance: there is no single "right" month to walk or sit. Each milestone has a broad, healthy range, so a child who walks at 11 months and one who walks at 15 months can both be developing perfectly typically. The WHO-GMM also gently notes that not every child crawls in the classic way — some bottom-shuffle or move differently — and still reach walking well. It is a population reference for typical development, used to understand patterns, not to label an individual child.

When to seek a review

Windows are wide, but they do have outer edges. Consider a developmental review if your child has clearly passed the upper end of a window without showing the skill — for example, not sitting independently or not walking by the ages your paediatrician flags — or if you notice your child losing a skill they once had, very stiff or very floppy movement, or strong one-sided preference in the early months. These are reasons to check in early, calmly, so that any helpful support can begin while development is most responsive.

The Pinnacle way

This is general information, not a diagnosis — a clinical AbilityScore® and any diagnosis are formed only at a Pinnacle Blooms Network centre, under qualified clinician care, never from an app or form. Our clinicians use references like the WHO-GMM alongside structured assessment of your child's whole movement picture, and where helpful build an individualised plan that may draw on occupational therapy and other supports.

Trusted sources

WHO Multicentre Growth Reference Study on motor development milestones and their age windows; WHO Nurturing Care Framework on early childhood development; CDC and HealthyChildren guidance on gross-motor milestones and healthy variation.

Next step — If you want to understand where your child sits within the WHO motor windows, book a gentle developmental review to map their movement strengths and start any helpful support early.