My husband went from a 640 to a 710 after taking the Veritas private tutoring program. He basically focused on math, which is what they are really good at and scored in the top 90% for the math section. (He was pretty good in the beginning and just needed some strategies for the DS though.)
So if you have a hard time in math, Veritas can help you a lot. In verbal, it's a coin flip.
But note that those who score really high usually have a high verbal score. It seems that a few extra points in verbal can result in a 700 going to a 730, but a few extra points in math keeps the score at 700.