going through my 6yo's test paper always ends in tears

he knows the stuff. when we sit at home he gets the sums right, reads the question properly. but in the test he finishes first and leaves half of it careless, wrote 7 for 17 twice on saturday's maths paper. the trouble is after. the moment i open the paper and point at one mistake his face goes and that's it, he's crying and saying he's bad at maths. i end up talking for twenty minutes and nothing gets through. i don't want to skip looking at it altogether. just want some way to go over it in five minutes without it turning into a whole thing. how do you all do it at this age?