Corrected entry: In the season 3 episode with Justin, the character who can see people's deaths, we are told he was born on the day of the meteor shower. This would make him 4-5 years younger than Clark and Lana (judging by their ages in the pilot), yet he is somehow in high school with them and getting the same homework. How can this be possible?
Correction: First, his name was Jordan. Second, it's been well established that Lana was 3 years old at the time of the meteor shower, so 4-5 years is just wrong. Third, it's established Jordan is a freshman, which Lana and Clark are not. Having the same class as other students doesn't mean they're in the same grade. And I often was a year younger than kids in my grade (without anyone skipping or being held back a year), so it's possible Jordan is a freshman while Lana and Clark are still juniors.
Correction: The kid had previously been home schooled so he could have easily been advanced for his age and there fore in a higher grade than most kids his age.