We did WJIII and portfolio for DS when he was in first grade, or thereabouts. The WJIII was from just before first grade, coming out of preschool (skipped K), when he was 5yrs 9mo, so it must have been in first grade or just after.

We just assembled a collection of stuff showing how he turned everything into numbers and math, and a "newspaper" that he made with a bunch of stories and weather report, stuff like that.