Transposing numbers, troubles with block design and puzzles can be a sign of a visual processing issue. A behavioral optometrist can evaluate and diagnose your child and design a vision therapy program for them, if needed.

Visual processing issues can cause discrepancies with performance and ability. It can cause perceptual problems, such as visual discrimination and memory. See
http://www.childrensvision.com/reading.htm

My ds6 has had vision therapy for 2 years and it's made a world of difference. He was born with some physical issues and visual deficits, which we noticed when he knew his squares and shapes but couldn't draw them. He had the Wechsler test this summer, but his test scores were too scattered and inconsistent, possibly due to visual processing issues. We're on the waitlist for further testing in the spring.

We were going to apply to DYS, but we're going to wait until the next tests. My son's behavioral optometrist told us about 1 1/2 yr ago that he was operating a couple of grade levels from examining him, though this didn't sink in until my son started visually multiplying last year and whizzing through the pre-k/k/1st grade curriculum in 2 1/2 months.