Three kids and three very different graduation parties here.
Our son (oldest child) did not want a party. He just wanted to get his diploma and get on with his life, thank you very much.

We had a backyard cookout with immediate family, grandparents and a few close relatives. He was happy and everyone enjoyed a relaxed afternoon.
Our middle child was the complete opposite. She has always loved any occasion to have a party. The more guests, the merrier!

We had two parties for her, both on the same day. She was in her glory, to be sure.

The first party (early afternoon) was for family, relatives and friends of the family, and the second party (late afternoon) was for daughter's high school friends. For the afternoon party, one of our daughter's friends acted as DJ. It was a long day, but lots of fun!
The parties were held in our yard, which has tons of space and a swimming pool. We rented a bounce house, a snowcone machine, popcorn machine, and cotton candy machine. We grilled hamburgers and hotdogs, had other finger foods, and two cakes (one for each party). The bounce house was a huge hit with all ages. In fact, I think the high school kids had more fun jumping and bouncing around than the younger crowd.

It worked out nicely, since our friends and relatives with younger kids had the bounce house to themselves before the older kids arrived for the afternoon party. No worries about little ones getting trampled by the bigger kids.
Our youngest chose to finish her last couple of years in high school by doing online courses/independent study. She was not at all interested in the traditional high school scene (her interest was in dance). She didn't want a party, but loves to eat out, so we celebrated by taking her to her favorite restaurant. We had a group of about twenty family members. Again, a different party, but also lots of fun.
Each celebration was different, but just right for each child.
