I strongly disagree with the assertion that inattentive-type ADHD is instead this “sluggish cognitive tempo”. It could very well be its own thing, as brain imagining studies show that SCT has a particular sort of brain activity abnormalities that are distinct from those that occur in ADHD-Inattentive. But dear lord, what an awful name – “your child isn’t slow, he just has sluggish cognition”. Ugh, it’s like when ADHD was called “minimal brain damage”.
Personally, I meet some criteria for the proposed SCT, like daydreaming, mind being elsewhere, and being disorganized, but those overlap with inattentive ADHD. I definitely don’t have overarching problems with mental processing speed. I excel at quick pattern recognition (won the first game of Set I ever played, against experienced players), and I’m quite good at spacial/visual thinking, abstract thinking, and related problem solving. I’m terrible at sequential thinking, though – I’d be the worst accountant. It’s not even that I’m slow at it, just… bad. I’m also not good at being articulate while speaking, so I hesitate or just don’t speak up, but during that hesitation, my mind is going a mile a minute running simulations about what I might say and how to best phrase it and how it would sound and gauging how the other person/people might react. I’m much better at writing. If I have trouble remembering/interpreting instructions, it’s because I wasn’t listening/don’t care, not because I’m slow at processing/registering the instructions.
I find the ADHD-inattentive = SCT theory pretty insulting in general because it’s essentially calling me slow and disregarding a lot of the nuanced aspects of my behavior and attention/reward-seeking that are already explained by ADHD. Hopefully recent studies that show significant differences between cognitive function between ADHD-inattentive and SCT kids will put that theory to rest and SCT can be designated as a separate thing like it should be.