Several factors correlate with English ability. Wealthy countries do better overall. But smaller wealthy countries do better still: the larger the number of speakers of a country’s main language, the worse that country tends to be at English. This is one reason Scandinavians do so well: what use is Swedish outside Sweden? It may also explain why Spain was the worst performer in Western Europe, and why Latin America was the worst-performing region: Spanish’s role as an international language in a big region dampens incentives to learn English. Similarly, the more Spanish-speaking Hispanics in the U.S., the less incentive there is to learn English, despite all those who try to convince us otherwise.
Teaching plays a role, too. Starting young, while it seems a good idea, may not pay off: children between eight and 12 learn foreign languages faster than younger ones, so each class hour on English is better spent on a 10-year-old than on a six-year-old. Between 1984 and 2000, the study's authors say, the Netherlands and Denmark began English-teaching between 10 and 12, while Spain and Italy began between eight and 11, with considerably worse results. Poor methods, particularly the rote learning seen in Japan, can be responsible for poor results despite strenuous efforts.
Finally, one surprising result is that China and India are next to each other (29th and 30th of 44) in the rankings, despite India’s reputation as more Anglophone. The Chinese have made a broad push for English (they're "practically obsessed with it”). But efforts like this take time to marinade through entire economies, and so may have avoided notice by outsiders. India, by contrast, has long had well-known Anglophone elites, but this is a narrow slice of the population in a country considerably poorer and less educated than China. English has helped India out-compete China in services, while China has excelled in manufacturing. But if China keeps up the push for English, the subcontinental neighbour's advantage may not last.
Working for logical immigation reform based on a stable population, a recognition of the finite nature of our natural resources and the adverse impact of continued growth on our quality of life, standard of living, national interest, character, language, sovereignty and the rule of law. Pushing back and countering the disloyal elements in American society and the anti-American rhetoric of the leftwing illegal alien lobbies. In a debate, when your opponents turn to name calling, it's a good sign you've already won.