|Success, measured by earnings or education, of immigrants in the US varies dramatically by country of origin. For example, average educational attainment among immigrants ranges from 9 to 16 years, depending on source country. Perhaps surprisingly, immigrants from Algeria have higher educational attainment than those from Israel or Japan. Also true is that there is a strong inverse relation of attainment to number of immigrants from that country. These patterns result because in the US, immigrant slots are rationed. Selection from the top of the source country’s ability distribution is assumed and modeled. The main implications are that average immigrant attainment is inversely related to the number admitted from a source country and positively related to the population of that source country. The results are unequivocally supported by results from the American Community Survey. Additionally, a structural model that is more explicit in the assumptions and predictions fits the data well.