A main source for the ages
WHO Motor Development Study: Windows of achievement for six gross motor development milestones
WHO Multicentre Growth Reference Study Group · 2006 · Acta Paediatrica
- Children
- About 800 children
- Where
- Ghana, India, Norway, Oman and the United States
- Ages
- 4 months to 2 years
- How
- Trained researchers tested the same children every month or two, and parents noted the dates too
- What it found
- The World Health Organization followed about 800 healthy children in five countries and measured when they first sat, crawled, stood and walked. Nearly all children walked on their own between about 8 and 18 months, and about half by their first birthday.
- Limits
- All the children were healthy and growing well, so the windows describe healthy children. The study stopped at 2 years.