My main concern, based on your description, is that these behaviors are of recent onset, and that he appears to be regressing in his academic skills, or at least newly inconsistent in demonstrating them. My first question would be, what changed in his life about two months ago? Curriculum? Type or difficulty of books he is reading? Family circumstances? His schedule? Sleep? Health? Extracurriculars? Growth spurt? You don't have to answer any of these that you'd rather not have out in public, but do think about them. Has anything else about him changed, other than his academic/cognitive presentation? Such as his mood, activity level, appetite, sleep habits, free play choices, etc.
The recent onset doesn't eliminate underlying learning disabilities or ADHD as the cause, but does introduce a large category of rule-outs.
Writing is in a different category, as you report a long-standing pattern of difficulty. What you describe does sound like there is something there to monitor, perhaps in the dysgraphic or fine motor delay category. Although expectations for six year old are pretty low, I'd still keep a close eye on this. With the level of reading he's had for a while, I would expect his spelling vocabulary to more closely approximate his reading vocabulary. Can he spell if he doesn't have to write it down (orally)?
