The report says they are behind in at least one developmental area, including physical health, language and cognition skills.
The report was co-authored by Dr. Cory Neudorf, chief medical officer for the Saskatoon Health Region.
Neudorf says the number may seem shocking.
He adds that kids are more vulnerable if they come from neighbourhoods where their parents have lower income and education, less employment and fewer social supports.
The report says in some neighbourhoods 10 per cent of children were not ready to learn, but in others the number was 57 per cent.