Looks like pyramids. But that may just be because I am a weirdo and…pyramids! Everything is arranged in pyramids whenever possible. Looks like upside down pyramids. I used to do that. But not upside down. Or I made things in general with my writing. Concrete poetry style. My sister also pushed her writing further over sometimes. Or writes really big. So that she has less room to write and is done sooner. She doesn't really do that anymore because she has to re-do it if anyone notices before she takes it to school. So…it could be deliberate. My sister was doing that in kindergarten and first grade. She is in second grade now. Age is irrelevant. High school kids aren't the only kids who try to weasel out of properly doing an assignment.

Remember that sensory processing includes visual processing — so it is not unheard of for a kid on the spectrum to have visual processing disorders, which can cause handwriting problems. In fact, with my oldest, it is one of the only noticeable signs of autism that he has. He has to use a computer in school for everything, and with standardized tests, he is allowed to circle in the booklet and it is transcribed for him. Other things are done for him orally, and so on. Years of OT and other therapies did not help, so now we accomodate. The only thing, though, is given that this is new for you, it should be brought up with a doctor next time you speak with one (neurologist). Also, if he gets any occupational therapy, bring it up with them as well — they have screening tests specifically for visual processing issues/writing ones. Lastly, there IS vision therapy, which is the one thing we did NOT try, because it isn't covered in our state AND is rather expensive. Hope this helps.
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My son, now 10, used to do this in Kindergarten. He is not living with autism, and is a typically developing kid. His teacher (we publicly educated back then) suggested using the highlighter trick. It worked. She suggested that he was doing it so he could finish his assignment sooner. IE, he would finish a page faster if he started each line farther and father over, or if asked to write a spelling word as many times as he could on one line he would be done sooner if e moved the margin. I called hogwash on that, as I didn't believe it was so intentional. I mean, really, that's high school mentality. We've all played with the margins to get the quota of "pages" for an assignment fulfilled, but not in Kindergarten. And not likely in Gavin's case either.

I have no clue how this relates to Gavin, but I think you should know it is not uncommon. Maybe it is just a step back. Your posts indicate you go through that often. I offer up this point of view only to try to help relieve some of your worry. I would say something at his next doctor's appointment, but I don't think you should worry too much about it unless the doctor seems to think it's related.

(Sorry Rob, the lingo here is all new to me, but I hope you can appreciate that like your mission statement indicates I am trying to become more aware. So if I say something not quite right, please forgive me, it will never be intentional.)

I've seen many kids loose the margin as they write, both kids with autism and typically developing kids. I tend to think that is caused by fatigue and lack of attention. Something you can try is to highlight the left margin with a bright color.