My DD14 graduated from 8th grade, and my oldest DD18 graduated from HS this year. They had a joint family/friend party. The older got lots of gifts, the younger got lots of cards and that was how it should be.
The reason we have 8th grade graduation is that the kids have attended the same parochial school since preK- so they have been a "group" for 10 years. At the end of 8th grade they split up- going to different high schools in town. The graduation is to celebrate the ending of one chapter and the beginning of a new- not a chance to get gifts. Friends and family who attend for the younger DD are "connected" to the school some how.
High school graduation, to me, celebrates the end of childhood schooling and the beginning of adult schooling or adult job holding- I think it serves almost as our nondenominational/nonreligious ceremony into adulthood. Very different- much bigger achievement and much more important.
That being said, if all things are on track, in 4 years we will have college graduation, high school graduation and 8th grade graduation at the same time. Good thing the littlest is two years younger rather than 4.....