G.B.
I would call her or stop by the classroom. It is the end of the year. They are having class parties, the mood is lax, it is nearly summer and kids are not paying attention.....
I suggest you consider getting some kind of tutoring this summer in math if he isn't able to do it.
I can honestly tell you that a "B" in math is not the end of the world. It is above average. An "A" is not average, if it were then it would be worth the 2.0 that a "C" is worth.
He may not have a gift in math but might in reading or science. Maybe he will always make "B"'s in math. He might be able to have a sudden light bulb moment too and suddenly math makes sense to him.
The teacher is just going to say have him do stuff like the homework he brought home.
I would start looking at online sites that have free tutoring or programs to strengthen the skills you don't think he has. That way you are looking at the stuff he had this year and what this program says a 2nd grader should know. That way you are reinforcing his existing knowledge and not trying to introduce new material he isn't ready for with out the foundation being there.