May I ask if your son's typing issue is hindering him in any way? There are several reasons he could be slower than you would like him to be........(are we talking about typing or handwriting?)........any mild learning disorder could result in slower speed, as could "lack of confidence", or being overly thourough.
But as far as problems go, I'd take this one over any problem with learning and remembering information and then applying that info in real life.
I sincerely hope schools where you are, are not placing an emphasis on this. Some people work slower than others.......there is no shame in this, especially since they are the same people who, more often than not, do superior work
Rome wasn't built in a day...........I hope you respond to this because I'm unclear what the problem is (is it typing?......is this the only problem?......did this concern come from you, him, or the school?)