Database: world_development_indicators
Question: What are the sources for the data of children who finished primary school education in North American countries?
SQL: SELECT DISTINCT T3.Description FROM Country AS T1 INNER JOIN Indicators AS T2 ON T1.CountryCode = T2.CountryCode INNER JOIN CountryNotes AS T3 ON T2.CountryCode = T3.Countrycode WHERE T1.Region = 'North America' AND T2.IndicatorName = 'Out-of-school children of primary school age, both sexes (number)'