I was one of these kids until high school. I actually made an overnight leap in math at the age of 15 and more or less "caught up" to where you'd expect my math ability to be given my global ability (I still consider it a relative weakness, but most people who know me would laugh at that). I also have a spatial weakness (possibly an actual learning disability), which has not improved.

Your child's situation may be very different, but what the math weakness came down to for me was that at lower levels, math instruction is execrable. I was homeschooled and my mother chose curricula like Saxon Math for me, which... did not help things, to put it mildly. It's endless, meaningless drill, taught by people who have no idea what math actually is.

When I went to public school in tenth grade (undoing my accelerations), I was afraid that I'd be hopelessly behind the public school students. But actually, I was lucky enough to get thrown into the formal logic unit in geometry... and even though the teacher hated math and didn't grasp what he was teaching on a deep level, it suddenly clicked for me. I got 100 on basically everything in high school math from then on, and the math chair made provisions for me to double up and take both trig and precalc in eleventh grade so I could take AP calculus as a senior.

I do find that I'm slower at arithmetic than most mathy adults, but just the experience of being thrown into a subject that was labeled as "math" but relied entirely on fluid reasoning and not on drill-and-kill made a light come on for me.

You may want to have your child read Lockhart's Lament and see what they think of it.