Title of this short story?

When I was a kid I read a book of mildly scary stories. Most haven’t stuck in my memory, but there was one I’d like to find again.

In it the world is pretty much like ours except that magic is an integral part of daily life. The story centers on one family, a dad and mom that have one son. They are worried because he’s not doing well in his magic classes, and seems to have no interest in them. All he wants to do is study his math. Kid gets bad reports from his teacher, and finally his parents take the step of summonin a demon whose job it is to scare the crap out of reluctant students. Confronted by the monstrous creature the kid squeals in surprise, grabs one of his math books, and, giving a command summons a mathematical spirit, one even stronger than the childhood demon. That critter is vanquished and the parents aren’t worried any more, knowing their son has the talent after all.

Anybody recognize this tale?

I don’t know the title, but isn’t that the one that ends with his shaken father saying

[spoiler]“Well if he wants to be an accountant that badly, I think we’ll have to accept it.”

If it is, then the creature he summons (who defeats the demon by means of quoting tax law) is “The Accountant” who’s been teaching him to take souls through legal loopholes etc.[/spoiler]

Still can’t find the title though…

Its not Robert Sheckley’s “The Accountant” is it?

I’ll look for the story based on the name and author. Thanks for the help! I do think that’s a line from the story, so you must have it correct. I also remember the demon laughing as he loomed up on the kid, booming out “A naughty little boy!”, or something like that.