I'm not an expert, just a parent, but I'll offer up a few thoughts.
First look - the Verbal portion of his WISC is his strength, and it's a good solid high number. While not PG, it would be high enough (most likely) to get him into a gifted pull-out in elementary school in our district. The first few years of elementary school are focused quite a bit on things that tie into verbal strengths, so chances are that a student with strength in that area might very well be under challenged in school, or bored if they were looking to school to be all about academic learning in the very early years. I'd also look at what's going on in his school - is it a traditional sit at your desk and learn to read school, or is it project-based learning, or something non-traditional? We have a lot of discussions here about what works best for gifted kids to keep them excited about learning when school can't quite meet their needs, but fwiw, the same applies (from my perspective) even to "average" IQ kids (which your ds obviously isn't).
Next thought - what do his subtest scores look like? Are they fairly consistent or do they fall all over the place (highs/medium/lows) within the same category? If there is a lot of inconsistency from subtest to subtest that can be a sign of not paying full attention/being distracted or some type of challenge/LD. Or just being tired - another thing to do is to google to find the order of administration of the subtests, then check to see if he's scoring lower toward the end of the test.
On the WIAT - I suspect that in most beginning first grade classrooms (which is where I think your ds will be in the fall?) you'll find there are some kids who are working at 2nd grade level, so he's most likely not alone in where he's technically at, if the WIAT scores are accurate. OTOH, it's also important to understand that, for example, a 2nd grade equivalent given with a WIAT score doesn't mean that the student is ready to work in 2nd grade in school; it means that the score is what the average 2nd grader scored on the same subtest.
You mentioned that you had him tested at 4 for a variety of issues - can you let us know what some of the issues were other than suspecting he was gifted? That might give a clue into possible reasons for low scores that aren't representative of his true intelligence.
One last note - one of my dds had a relatively large drop (approximately 20 points) in IQ when tested at 5 (higher) and 7 (lower). I don't really know which is accurate to be honest - I've been around enough technically "gifted" kids to know that it's just not possible to predict actual IQ based on vocabulary, thoughts shared, etc. At least not for a parent like me
One of the most successful high school students I know (all-around, high-achieving) is the dd of a friend who, when her dd was 5-6 years old, was convinced she was PG based on the thoughts she shared with her mom and the academics she was completing. Once she had an actual IQ test it turns out her true FSIQ is around 120 - but her mom never stopped advocating for "more" for her just because she wasn't PG. Neither should any of us parents - you have to trust your gut, go with what you see as your child's needs, and advocate to see that he gets appropriate challenge in school. If you have reason to suspect 2e hiding abilities, dig deeper.
And even if this is his actual accurate profile, that doesn't mean he doesn't need challenge in school. When you meet with the school, be sure to focus on samples of his work (from class and at home), and what he is telling you about school. He may not have sky-high gifted scores, but he's got good strong solid scores, with a strong Verbal score and a reason (possibly) to suspect the scores might not be representative of his true abilities.
Best wishes,
polarbear
