What did the rest of his WISC-IV profile look like? I assume the WMI and PSI were somewhat comparable to his VCI and PRI, since the FSIQ is in the same range.
1. Reversing letters is not a huge red flag, per se, at this age.
2. Misspelling words suggests that he has been learning to read predominantly by sight, not by phonics, which may be why he made a sudden leap recently, to the late second-grade level (he probably memorized the majority of the Dolch list/high-frequency words, which comprise about 60% of typical English text, thus giving him access to a great deal more reading, and substantially more fluency). This is more of an indicator of possible stealth dyslexia. The phonetically-reasonable spelling error that you gave as an example suggests that he has rudimentary phonological processing and phonics skills, but lacks the more sophisticated skills. This often means that grade-level testing will not pick up his deficits, since the PP skills that will expose his possible weaknesses are the higher-level ones expected in older students (such as phoneme manipulation tasks--phoneme reversal, substitution, deletion).
3. His writing speed may or may not be a function of fine motor development alone. There are many factors that can affect that, not exclusively dyslexia. For example, vision, visual-motor coordination, retrieval efficiency (of letter formation, or of spelling), fatigue, inattention.
4. This is another indicator that he probably reads by sight, not by phonics. Also suggests that motor coordination may be a factor, since oral-motor coordination is necessary for reading aloud. To be fair, it is also true of fluent readers in general, that silent reading is faster than oral reading. I don't think many of us can sustain oral reading at 300+ words per minute. (The average adult reads 250 wpm, silently, and there are probably quite a few people on this board who can read 400-800 wpm.)
I think it would not be unreasonable to pursue assessment for stealth/compensated dyslexia, though it is, of course, possible that the process of learning to read for him is just taking a slightly different path from others, but will reach the same destination. If you pursue an evaluation, you will want to start with a psychologist experienced with 2e individuals. When you approach a prospective evaluator, you may wish to include in your assessment question concerns about his ability to decode novel words, and whether he has the underlying phonological processing and automaticity skills to be able to progress in basic reading skills at a level commensurate with his extremely high verbal ability. Though not a major issue in the primary years, it may become an obstacle as the volume and complexity of reading increase, and speed becomes a factor.
The kind of assessments involved in a stealth dyslexia eval, in addition to the WISC-IV you already have, may include:
1. Phonological processing: e.g., CTOPP/CTOPP-2, PAL-2, some subtests from the WISC-V, WJIII/WJIV, KTEA-2/KTEA-3. In particular, you want higher-level tasks involving phoneme manipulation, not just the low-level blending (c-a-t makes cat) and segmentation (cowboy is made up of cow-boy, or, slightly higher level, cat is made up of the sounds c-a-t) tasks.
2. Phonetic decoding: nonsense word or pseudoword decoding tasks, such as the subtests with those names from KTEA-3, WIAT-III, WJIV, PAL-2. This is distinct from reading lists or passages of real words, which he will probably do rather well, using sight vocabulary.
3. Oral reading fluency: measures of speed, which, in high-functioning dyslexics, often stand out as discrepant from the level of reading accuracy using real words. There are subtests on the PAL-2, WJIV, and KTEA-3 (also on the WIAT-III, but not at his grade level). The GORT-5 is an in-depth measure exclusively of this skill and related skills.
4. Reading comprehension: subtests of the KTEA-3, WIAT-III, and WJIV, among others (in order of my preference). An excellent stand-alone measure is the TORC-4. Mainly interesting to demonstrate any possible discrepancies between reading decoding and reading comprehension skills. I would expect this to be relatively higher.
5. Be open to wider-ranging assessments, as often the behaviors of concern can be interpreted in many different ways; one doesn't want preconceptions to blind one to a more comprehensive understanding of his learning profile.
