Numerical estimation in individuals with Down syndrome.

Lanfranchi et al. (2015) asked how kids with Down syndrome place numbers on a blank 0-100 line. They compared the group to mental-age-matched typical kids, not same-age peers.

The team used a simple paper number-line task. Each child marked where they thought a spoken number belonged.

Children with Down syndrome made marks in the same pattern as mental-age peers. Their estimates grew straighter as mental age rose, not as birthday count rose.

The shape of the line told the story. Kids with similar thinking skills produced similar lines, no matter who was older.

Lanfranchi et al. (2022) ran almost the same task seven years later and saw the same thing. Mental age again beat calendar age at predicting accuracy. The newer paper added that kids who could name digits 1-10 and pick the bigger of two numbers 1-20 drew straighter lines.

Lawer et al. (2009) mapped 88 French children with Down syndrome and found four clear cognitive profiles. No profile followed age, echoing the idea that thinking level, not birthday, drives performance.

Gomez et al. (2015) looked at kids with developmental coordination disorder and saw the opposite comparison choice. They lined up participants by calendar age and found deficits. Silvia’s mental-age match shows what happens when you compare thinking level instead.

Stop waiting for a child to reach a birthday before teaching number lines. Check mental age or simple digit naming first. If the learner knows digits 1-10 and can spot the bigger pile up to 20, they are ready for the 0-100 line. Start there and move forward.