Blackcat-- It's in there, he just can't pull it up in the moment with the pressure of being asked to "perform".
My DD was very similar - eerily so.
Further practice, which increased fluency and confidence was the only thing that helped overcome the perfectionism - see previous post on drills. Also, working through the SM and the Zaccaro challenging Maths without a calculator helped.
The final thing has been the AoPS pre-algebra class, especially their coverage of the properties of the arithmetic operations and number theory.
The speed with which my DD can cover material always leaves nagging doubts about how much of what she has apparently learned will stand a vigorous shaking. What I have seen of the AoPS pre-algebra class helps to quell those doubts.
