Is it really *that* bad if a child uses the term "take away" instead of minus?

The school year is over, and my nephew that lives with me is going in to the 6th grade, so technically Jr. high and he finished with all A's and ped his TAKS tests with all A's, so he is a very bright boy. His teacher has a huge problem with him using the term "take away" when talking about subtraction. So he will say 5 take away 2 instead of 5 minus 2. She says its immature, and he absolutely should not use it when in Jr. high. I don't get it. How is it that big of a deal. She has been harping on him all year about this, and I don't often use the word minus in daily life. If I need to subtract something, I do it on paper or in my head you know? So I'm not spouting off the word minus very often. Its made him embarred to go to the board and work out problems, and he says she always called him to the board to work the subtraction problems, and make him recite the problem, and then scold him to use the word minus. He says he tries to, and he means to do it, but "take away" comes out instead and he corrects himself. Long I know, but is this really such a big deal? Will he be made fun of or fail simply for using the words take away? Of course the kids don't make fun of him for doing it, but to hear his teacher talk, its the worst thing ever, like he is a huge baby.