My 11 year old is very similar by the sounds.
So far she's got away with it.
I don't believe she has a medical or development issue. She's just bloody awkward. Won't do things until she decides it's time to. It's been apparent since she started weaning/potty training. And goes on.
I did used to wonder if she had a problem with fine motor skills. Writing was such a chore. But then in Year 4 I think it was, you could have a pen at school to write with, as long as your handwriting was neat enough. Overnight her handwriting improved into a beautiful script. She was awarded the pen, then reverted back to a sort of lazy scrawl straight afterwards.
So far she's managed to get away with it. But I do wonder what she could achieve if she actually tried. She's good at maths, understands all the grammar. She reads avidly. Spends hours typing out stories on the computer at home. But produces the absolute minimum at school when it comes to writing. She's in top groups for everything however.
Homework is painful. If it's easy, it gets done in 5 minutes. If it involves any effort (e.g. reading a passage/instructions) it gets thrown across the room with much stamping/shouting.
My MIL has only recently told me that dh was the same. I can see it in his personality actually now. He only does things if he wants to. That can be a lot later than other people decide, actually it might be a good idea to do this now.
Dh did well with O/A levels. Then flunked his degree. Then went and did another degree ten years later which he excelled at.
So I'm marking my place here and sympathising.