Cubans are different from other Latin Americans in a few important ways. One of them is that their indigenous population was wiped out. They still have some people of mixed blood, but they are basically either white or black, or mixed black and white. Their indigenous populations do not exist in nobody's living memory. Listen to their music, see their traditions, and you won't find the indigenous ancestry that is so evident in, say, Bolivia, Peru, Guatemala or Mexico. They are different even from Puerto Rico.
This means that they had a different make up to start with.
Second, Cubans who live in the United States are often people who fled Castro. Those people were usually the better schooled in a country whose educational average was, at the time, also higher than elsewhere in Latin America (or Spain, or Italy, by the way). Besides, Cubans knew and still know that they just cannot return to Cuba. They have to make it in the United States or die. Besides - and this is not a small difference - they knew they were there to stay. How many Cubans would be deported to Cuba, compared to Mexicans or Salvadorians?
In contrast to Cubans - at least to the first wave of them - Latin Americans from other countries who move to the United States tend to be those who cannot make it at home. Cubans who fled Cuba were those who knew they COULD make it abroad.
We Latin Americans are a very disparate lot. The Dominican Republic shares a lot with Argentina, or Peru, but they are also very different countries. The Dominican fiesta is very different from Andean melancholy. That is true. I am not of Cuban descent and am speaking of Latin Americans of other descent.
I have several relatives in the United States, from two different countries, and they are very different. Two are Police officers in Los Angeles. They were born in the United States and their family has probably been there longer than anybody else. One of the brothers is an agent for movie stars (not the famous ones). A grand-uncle in Miami is a neurosurgeon. He makes very good money and his children, who were born there, are also professionals. This family is well-off. Another relative is a dealer in Las Vegas while his sister works in the court as a translator. You can see that even within families, personal situations are very different, because everyone responds differently to the great cultural shock that comes with moving to the United States.
Some friends of mine went there and were quick to have anchor children, because they wanted to be sure they could stay. Now that doesn't count, but, at the time, it mattered. Starting off in a new country with a new kid is a very different thing from starting off alone, yes, but knowing you can stay.
But I still believe that, while starting out with a disadvantage matters, it does not explain our failure as a group. I think it has to do with simple parental interest in your getting an education. And also with personal interest.