I disagree. You're talking apples and oranges.
Take Jews coming from the Russian Empire in the 1800s for example. Fairly large group of immigrants. They may have come over with nothing but a suitcase, but their families have probably had formal education for centuries, with a 90% literacy rate (granted, this is unusually high for most immigrant groups). Back home they were part of an established society, with culture, laws, their own courts, etc. They've had well organized family structures probably going back to Biblical times.
Or take the Irish, a huge group of immigrants. Most of them were dirt poor. But again, almost all have had some compulsory education. You have a society that has been around for a thousand years, with established family structures, and even political organizations active around the world. Not to mention, an extremely high proficiency in English.
Now, Asian and Hispanic immigrants had it harder, due to racism, and the language barrier. But again, you do in most cases have a history of education, well established family structure, etc.
It's really the centuries of education, the accumulation of capital, culture and knowledge that make the biggest difference.
Most African Americans had none of that. They were robbed of all of it.