A word of caution here. The Grades don't always mean a certain age.
Years ago, I did a "Show and Tell" for my New Hampshire friends local school. Her daughter was about 7-8. I noticed that 2 boys seemed to be considerably bigger than the rest of the class. When I enquired about this to the Teacher, she said that those 2 boys had not graduated from the Grade last year and they had to do it again. I'm not sure at what point this sort of thing stops, as it doesn't make sense for hulking great lads of 11 to be still in the lower grades !
Actually, the "Show and Tell" came back to haunt me years later. The kids had never met anyone from Wales before, so they were very keen to know all about Wales. I told them what things were like here...what we ate, our customs, etc. We got on the subject of animals. Now, in that part of New Hampshire, they have bears, moose, poisonous snakes, raccoons, etc. I wasn't going to let Wales be outdone, so I told them that we still had dragons, who lived in the mountains of Snowdonia, and that was why we had a red dragon on our flag ! The kids lapped it up ! Their eyes were like saucers.
About 12-13 years later, the daughter of my friends had a boyfriend round for the afternoon, a huge great bearded 20 year old, and he told me that he remembered me from that "Show and Tell" all those years ago. He asked me if there really were dragons still living in Wales. When I hesitated for a few seconds before replying, he gave me a broad grin, and said he thought I was pulling his leg ! But he did say that part of him DID believe in dragons, up until he was at least 16 years old !