You've already had more thorough advice than I can give... But I thought I would add another annecdote.
My DD did the WPPSI at 4y9m. Her VCI was 142, PRI either 135 or 138 (mum's memory is shot). Coding was 10.
Now at the time I put this 10 in coding down to the following:
a) the tester did not tell her it was a race to see how much she could do and that she needed to do as much as she could do before the time went
b) it was boring as and she was over it all by then.
She did each item twice (correctly), clearly felt she had proved her mastery and then sat and watched the timer for the second half of the time available.
We now know that she has a handwriting disability. She has congenital low tone and ligament laxity, with an extremely mobile thumb, she literally can't hold a pencil adequately without a brace to immobilise her thumb. So maybe she stopped purely because it hurt, and who wants to do a boring & repetitive task that hurts, or she just didn't like writing. Or maybe it was a mix of all three.
My point is that knowing my child well reasons a & b made perfect sense and completely explained her low score to my mind. But in retrospect it may also have been a disability at play...
