Son just graduated from Swarthmore and works for HeadFirst over the summer. Take the tests as early as you can. With rare exception the schools will only look at your best score on each section at each seating ("superscore") and disregard the rest. SAT II's are more important than you think and more important than the schools will tell you to your face. Take them right after you've taken the respective school course (i.e. American History June Sophomore year, etc.). The Math SAT II's have higher value than the others especially for prospective science and engineering students. For high academic coaches, you really don't even exist without test scores and grades. Most importantly,you need to present a challenging course schedule. That's the starting point. Then baseball.
The Delta between SAT and ACT is usually small (90%) but unfortunately, since you don't know if your student is in the 10% with a significant difference, many high academic kids end up preparing for both and then taking both. This is a terrible system! 700 is your target for each section of the SAT. Scores above that stop helping (Son had a perfect verbal score and when a director of admissions told him that he didn't care, son was shocked and depressed). Over-testing doesn't help. Generally, after 2 sittings its time to admit, as Bill Parcells says, "you are, what your score says you are."
The writing section of the SAT was very subjective so most schools ignored it and looked for other evidence of writing skill. It is eliminated in the new test, but ignored in the old test. Don't worry about the new test; Adcom's are well prepared.
Hope that helps.
I lecture at an Ivy, played a sport at a Patriot, and kids played at high D3's so I can answer any academic questions you might have about the process.