For those parents here whose children have achieved impressive Math SAT scores at an early age -- how did they prepare?

I'd guess that in many cases, the child has a high level of talent and motivation in math, so that he/she can study algebra by late elementary school. Once a child has exposure to algebra and some geometry, he/she has the math background to do well in the SAT if he/she has the talent.

"To see what is in front of one's nose needs a constant struggle." - George Orwell