system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 Why school systems don't divide students based on ability rather than age

Edit: so many karmas but no karma added :( thanks for all the great responses and front page!
gpt
They already do to an extent; most honors and AP classes will have students from a couple different grade levels.  
  
However, the reason that this isn't done all the time is because school isn't purely for academic learning. It is also important to learn social skills too. For school age children, there is lots of growth between each year. It would be harmful for a 14 year old to spend the entire day around 12 year olds just because he isn't good at schoolwork.