Yup Laugh it up...
Sorry, I couldn't help myself, this is comical on so many levels. First off, a MINUS 20%? I mean, c'mon you can't possible score below zero. Then the LOSER part *DEAD*
Ok, so now that we are past the headline and got our giggles out we can really analyze this. Personally, the sensitivity of this issue would lie in the age of the student. For example, a teenager/high school student this would definitely be a character building moment. If you got that far along in the education system but turn in work where you don not get a single answer right? That would be loser-esque. Hey, the student may not be a loser but they would be on the loser path FOR SURE.
In actuality though that is not the case. This was handed out to a 6th grade student, probably age 11. To me this would warrant anger from the parent. At that age you are still fairly early in the learning process. Labeling a child a loser could be quite damaging especially coming from a teacher - whom children should look up to. In the video it is stated that the teacher has a method of teaching that is a way for him to better relate to the students. It is also stated that many other parents supports this method of teaching, though they did not want to go on camera stating that.
There is definitely more than meets the eye to this story. Nonetheless the angered parent could simply request their child be placed in a class with a different teacher - she probably did not do that because all the other parents and student say this teacher is great. It is also possible that the school and town are so small that there is only 1 teacher for that grade and subject - thus the only option. This is not the first student that this teacher has graded a "loser" and could possibly just be the case of an overzealous parent who need to find a tutor for their child.
But hey that just my opinion....