Nearly a third of foreigners wanting to make Britain their home failed their citizenship test in 2009, figures show.
Of the 906,464 people who took it, 263,641 failed - meaning the pass rate was 70.9%, Home Office figures show.
The 45-minute test on British society, history and culture is a crucial step on the road to being allowed to settle permanently or full citizenship.
Nationalities with a pass rate below 50% included Iraq, Bangladesh and Turkey - all major sources of migrants.
Some 40,200 Iraqis sat the exam, with a pass rate of 47.9%. Among the 30,014 Turks who took the test the rate was 45.9%, while out of 38,085 Bangladeshis, 21,345 failed - a pass rate of 44%.
Those from other non-EU countries with high levels of migration to the UK performed better, including Nigeria, with a pass rate of 82.5%, and Zimbabwe with a pass rate of 90.2%.
Citizens of English-speaking countries tended to do best in the 24 question multiple-choice exam.
The 13,223 Australians who took the test had a pass rate of 98%, just ahead of the United States on 97.9% and Canada on 96.9%.
Several countries achieved pass rates of 100%, although the very small number of candidates tended to skew the results. The Cook Islands' sole entrant passed.
Similarly, there were some very low pass rates from countries with a handful of candidates sitting the test - five out of the six French Guyanans who sat the test failed, giving them a pass rate of 16.7%.
And the Christmas Islands had a 100% fail rate, thanks to the failure of its sole candidate.
The Home Office's Life in the UK Test is required for settlement, or indefinite leave to remain, in the UK or full British citizenship.
The test must be completed on a computer at one of 11 test centres around the UK.
Introduced in 2005, the test is meant to help new arrivals hoping to make Britain their home integrate better into British society.
It covers issues such as Britain's constitution, the originating countries of previous UK immigrants, family life in the UK and where dialects like Geordie, Scouse or Cockney come from.
More practical matters such as the minimum age to buy alcohol and tobacco and what services are provided by local authorities are also covered.
According to the Home Office website, "studying for and taking the test will give you the practical knowledge you need to live in this country and to take part in society".
Passing the citizenship test demonstrates the candidate has "a sufficient knowledge" of the English language for the purposes of applying for settlement rights or a British passport.
The test is an alternative to completing an English for Speakers of Other Languages (ESOL) course "with civic content".
It comes as separate Home Office figures show the number of people granted British citizenship last year is at its highest level since 2005.
Figures show 203,790 people were given citizenship in 2009, up 59% from 129,375 the previous year.
There was also a 40% increase in the numbers given grants of settlement in the UK and a 45% rise in those allowed to settle for employment reasons.
The data comes from the International Passenger Survey of long-term international migration.
Explaining the large gap between the number of people who passed the citizenship test and those who were granted citizenship last year, a home office spokesman said there was often a "time lag" between passing the test and applying for citizenship.
In addition, he said passing the test did not guarantee citizenship and some applicants were refused it "on other grounds".