Why is there 8th grade at Abbott?

Hey guys, I'm fairly new to to sub but have been watching Abbott since the beginning. It piqued my interest because I'm getting a dual degree in elementary education. With that being said there are some inaccurate things in the show I can pick out right away but I ignore them because this is literally television.

The one thing I can't shake is the egg drop episode when the 8th grade class is holding their egg drop contest. It is assumed that there is an 8th grade class here at Abbott because they encounter this teacher regularly. My question is, was there a logical explanation in the show for why this is and I just missed it?

I want to make it clear that I know some elementary schools go to 6th grade but I've never seen them go all the way to 8th grade. That is essentially 5 year olds and 14 year olds at the same school.

**Edit

Just to clarify I went to a k-8 school before so I know they exist. It's just that they explicitly call it "Abbott Elementary" that threw me off. None of the k-8 schools where I'm from ever call themselves an "elementary" or "middle school" so that confused me.