This article was in today's PI about 9th graders being able to take the 10th grade WASL. The number doubled this year from about 6500 last year to over 14,000 this year. My son was one of them. He took the Reading and Writing. (We decided against the math and science. He hasn't had year-round science and we decided to check out the 9th grade practice WASL in math first even though my son is in honors math.) He thought the reading and writing were easy. My husband and I just thought he might as well get it out of the way and be able to do more work on other subjects next year.
It does count as one of the tries but if, on the other hand, you really wanted to see how your student was doing, taking it sooner could be an early warning system especially if your student scored 1s instead of2s or 3s.