DS (4.75) reads, we guesstimate, at around a grade 3/4 level. He is skipping K and going into grade 1 next year. My brother is a teacher and has suggested the highly experienced GT lady at his school informally assess DS to find out his exact reading level to give us a better picture of what we are dealing with for next year (she has offered). We don't plan to IQ test until 6 or 7 since the school didn't require it. Do you think this would be useful? I assume his school will want to do it and it will be higher by next year anyway, given the leaps in the last 6 months. I trust my brother but don't know if this offer is fascination on her part or just because she has known my brother for years and feels it will really help.

Seems like the best use of that information (since you've already decided to skip), is to select appropriate reading for both fluency/comprehension practice and a level higher for a challenge.

I didn't know where my ds5 was...I did some online searching . I found vocabulary lists that helped me see his reading vocabulary words are at a very high level ( 6th grade or more), but he is not reading there of course (but it was fun to know anyway :)). We just borrowed books from the library at different levels and discovered which ones he could read fluently vs. which ones created a small challenge (missing one word a page).

He loves science books, and we get whichever book catches his eye no matter the level. I work with him on the challenge-level books (which are more fictionbased as opposed to fact captions like science books).

I would have it done. If she is highly experienced, I don't think that it would just be fascination on her part, she's likely seen enough children like yours for it not to be a novelty.
I think it would be a good idea, especially since it is coming from their end!

We have decided to go ahead after DS picked up a grade 5 reading/comprehension book and read the first 2 stories with no concerns (and could answer the questions). Maybe we have underestimated his level too...