it could be his mind is picturing the equation as 27-14 instead of 14-27.
cos we have been introduced to this maths world through the method of "counting fingers" and all elementry calculations involve +ive result. (ie. "folding down" the fingers to denote minus).
Therefor its time for him to learn new concept (-ive result).it might be quite difficult at first cos there will not be any tangible visual aid for -ive number. just be patient. :)