Unless you are rehearsing at 7 am, the south or west are the LAST directions the students should be facing. As the sun moves through the day it tracks to the south (as the season progresses the sun will sit lower in the south...as opposed to right now where it is closer to being overhead), and in the evening, the kids will be staring right at the sun facing the west.

Have the kids face the north, and the sun will be at their backs or to their left.