You've received excellent advice from spaghetti, and I'll add that your ds is still quite young - it's possible that what you're seeing is a result of an issue that would only need to be addressed by OT, or it might be an indication that something more is going on - it's very difficult to tell sometimes when a child is only 4 and is just starting out in a school environment.
However, many of his behaviors at school, don't line up with how he behaves at home.
This can be true even if there is a challenge - the tasks a child is required to do at school are often different than what he does at home, and sometimes at home a child simply doesn't do things he's challenged with, and a parent would never realize it because we don't push our kids to do those things. I have two 2e kids, and had no idea either had a challenge until they went to school - yet the symptoms had been their all along, it just took the ability to know what was up and look back in hindsight to recognize them.
He'll follow a long set of Lego instructions and put together tiny Lego pieces, yet he doesn't always listen in class, gives up on lacing patterns and just wants to scribble when asked to color in lines. He can read chapter books, but he gets extremely flustered when trying to open bathroom stall.
Being able to accomplish one task successfully doesn't mean their isn't a challenge present that's impacting his ability to accomplish a different task. I'll use my 2e ds as an example, but I have no idea if his situation relates to your ds at all - it's just an example. My ds has DCD. He was able to put together complicated lego pieces at an early age, as well as creating tiny tiny intricate figures from clay. He's also very good at drawing. He didn't learn how to tie his shoes until he was in 4th grade, and even then he forgot for awhile and had to relearn how to tie. He has fine motor dysgraphia, and in spite of being able to draw well couldn't learn how to write his letters - so when he was required to write at school, instead of telling someone he couldn't figure it out, he threw tantrums, crumpled up his papers, and just didn't do the work. By 2nd grade he was basically "checking out" in class - appearing to not pay attention. I could list more examples, but the basic thing to understand is: 2e kids (and really, most kids) don't come with an obvious across-the-board challenge or an obvious across-the-board brilliance, for 2e kids you'll see a mix of abilities and as parents when our children are very young we tend to focus on and recognize accomplishments rather than noticing challenges.
You're going to talk to your pediatrician, which was my first suggestion. Ask what his/her perspective is on whether or not to seek OT within the school, outside the school, or look into something more than OT. You can proceed with an OT eval whether or not you eventually look for a psych-ed or neuropsych eval - it will provide data that the psychologist will be interested in seeing.
Would OT assessment miss some other areas where he struggles?
Possibly. I'd think through all the areas you feel he's struggling, list them out, talk to your ped. I'd also ask your ped's opinion of the benefit of OT inside/outside school where you live - school services can vary quite a bit from area to area. My other caution about school evals is the school is only evaluating for impact on academics/in the classroom. It's quite possible to have a challenge that's limiting yet doesn't meet the bar of what it takes to qualify for services at school, or to have a challenge that isn't recognized during the course of a school eval. I'm not saying that to dismiss school evaluations, just have experienced that first hand in our school district.
FWIW, I'd google DCD or dyspraxia too, just for reference to see if any of it seems to fit. Much of what you wrote sounds a lot like my ds at that age... but again, I'm only a parent, not a professional.
Best wishes,
polarbear
