The College Board publishes a “Total Group Report” for each year’s SAT. For 2015: https://secure-media.collegeboard.org/digitalServices/pdf/sat/total-group-2015.pdf
You’ll see the results from each senior’s last SAT exam listed on page 1. The highest scoring group of students is…
Sophomores.
Now, there are only 5,579 of them, but as a group they post the highest averages. So there is a group of very high-scoring students who take the SAT as sophomores, then find they don’t need to take it again.