I believe that you can use scores from before a child's 5th birthday, but that your child must be 5 to submit an application.
DYS DS took the WJ Ach. at 4 for an extra-curricular enrichment program, and the biggest benefit was the high ceilings. When DS was tested at 6, the tester recommended the WIAT. While the tester felt this test is more "child-friendly," DS hit some ceilings. So for him, the WJ might actually be a better test.
I think one of the trickiest things you might run into at that age is getting composite scores. It seems some subtests might not be normed for very young students. Make certain that your tester is aware of your need for a test, with DYS-appropriate composite norms available for your child's age. I seem to remember that the WJ may had some issues here, with percentiles not available on composites up to the 145 minimum at age 4.
Still, we were able to use the WIAT results for DYS.
Best wishes!!!
