There should be a grad after grade 12 not 8 becasue you still got school after grade 8.
Well, benben714 is sorta right...it symbolizes going from middle school (at least in the states) to high school, which is much different.
Some places even have pre-school graduation, kindergarten graduation, elementary school graduation, middle school graduation AND high school graduation. It's just to symbolize moving up to the next tier of education / schooling. (Speaking for the US).
Yeah here in Canada where i am we have Elementary School which is K-8 in most cases, and then high school which is 9-12, so there is a graduation to symbolize the achivements in Elementary and then again at the end of highschool
there is graduation after grade 8 because it symbolizes you moving from elementary school onto highschool where i live in ontario, we also have graduation after grade 12 because this is your final highschool year