W HEN WINSTON CHURCHILL was at Harrow School, he was in the lowest stream. This did not, he wrote in “My Early Life”, blight his academic career, for “I gained an immense advantage over the cleverer boys. They all went on to learn Latin and Greek and splendid things like that...We were considered such dunces that we could learn only English...Thus I got into my bones the essential structure of the ordinary British sentence—which is a noble thing.”

Partly thanks to Churchill and the post-war Anglo-American ascendancy, English is these days prized, not despised. Over a billion people speak it as either their first or second language; more still as a third or fourth language.

English perfectly exemplifies the “network effects” of a global tongue: the more people use it, the more useful it is. English is the language of international business, law, science, medicine, entertainment and—since the second world war, to the fury of the French—diplomacy. Anybody who wants to make their way in the world must speak it. All of which has, of course, been of great benefit to this newspaper, which has floated on a rising linguistic tide.

It is not surprising that there is a surge in “English-medium” education all over the world. In some regions—such as East Asia and Latin America—the growth is principally among the rich. In others—Africa and South Asia, where former colonies never quite escaped the language’s grip—it is happening at all income levels. Parents’ desire for their children to master English is spurring the growth of private schooling; parents in the slums of Delhi and Lagos buy English-medium education in the hope that their children will gain a university degree, obtain good jobs and even join a glittering world of global professionals.

Where the private sector leads, governments are following. Some countries have long chosen to teach in English as a political expedient, because a local language would prove contentious. But even where public schools teach children in their mother tongue, or a local language, education authorities are switching to English medium, in part to stem the outflow of children into the private sector. That has happened in Punjab and Khyber Pakhtunkhwa in Pakistan; many Indian states have started large or small English-medium experiments. In Africa most children are supposed to be taught in a local language in the first few years, but often, through parental pressure or a lack of textbooks, it does not happen.

Teaching children in English is fine if that is what they speak at home and their parents are fluent in it. But that is not the case in most public and low-cost private schools. Children are taught in a language they don’t understand by teachers whose English is poor. The children learn neither English nor anything else.

Research demonstrates that children learn more when they are taught in their mother tongue than they do when they are taught in any other language (see article). In a study of children in the first three years in 12 schools in Cameroon, those taught in Kom did better than those taught in English in all subjects. Parents might say that the point is to prepare children for the workplace, and that a grasp of English is more use than sums or history. Yet by year five the children taught in Kom outperformed English-medium children even in English. Perhaps this is because they gain a better grasp of the mechanics of reading and writing when they are learning the skills in a language they understand.

English should be an important subject at school, but not necessarily the language of instruction. Unless they are confident of the standard of English on offer, parents should choose mother-tongue education. Rather than switching to English-medium teaching, governments fearful of losing custom to the private sector should look at the many possible ways of improving public schools—limiting the power of obstructive teachers’ unions, say, or handing them over to private-sector managers and developing good curriculums and so on.

Pakistani Punjab has decided to end the English experiment; Uganda has introduced mother-tongue instruction in 12 different languages in the first four years of schooling. More should follow. After all, it was a good education in his mother tongue, rather than in the classics then favoured by the British aristocracy, that won Churchill the Nobel prize for literature.