Does where a student comes from relate to how well they'll perform in an English language program? The results of a recent longitudinal study say, yes (Colon, 2018).
However country of origin only accounts for 1% of the variance in completion rates. Meaning there is a variable (or variables) out there that are a stronger indicator of success.
None-the-less the descriptive information is notable. From 2004-2014, U.S. English language program completion rates for the leading ten countries of origin for enrollment varied:
South Korea 35%
Japan 56%
Saudi Arabia 16%!
China 22%
Taiwan 51%
Brazil 65%
Thailand 23%
Turkey 39%
Colombia 57%
Mexico 69%
Although not a leading country of origin for enrollment, Switzerland had a notable average completion rate of 92% Consider these rates in the context of the overall English language program completion rate of 40%.