Seems like there are many possible source for a lowered processing speed. If the source is more in the perfectionism or executive control area (prone to overthinking/reworking, thinks too much, easily distracted in thinking), I'd imagine that it could improve over time with maturity and/or other controls.
This is my DS... his processing speed was in the 21st percentile, accompanied by "difficulties with sustaining attention and following instructions." I've noticed a big difference in this area in the year since he's been tested and am really curious to see if the PS has increased. (Oh well, no $$ in the budget for it at the moment).
I think when they're young it can be tough to get an accurate result. It depends on the child and the nature of the interfering behaviours... I just know our doc said "take it with a grain of salt."
