The report looked at 41 million foreign-born people — including about 11.3 million immigrants here illegally — and their children born in the United States, about 37 million Americans. Taken together, the two generations include one in four people in this country. English language learning “is happening as rapidly or faster now than it did for earlier waves of mainly European immigrants in the 20th century,” the report found.

Many immigrants — about 85 percent of the foreign-born — speak a language other than English at home. For 62 percent of them, that language is Spanish. But many of those immigrants speak English proficiently outside the home. Many already knew English when they arrived, the report found; about 50 percent of the foreign-born say they speak English “very well” or “well,” while only 10 percent say they do not speak English at all.

By the third generation, most immigrant children speak only English, the report found.

In a finding the scholars called surprising, the report says foreign-born adults and children are healthier in general than Americans. They are less likely to die from cancer or heart disease, and have fewer chronic illnesses and lower rates of obesity.