Did I wrote the sentence correctly?

"The knowledge they receive from parents can be an extra."

(What I mean is that the knowledge children receive from parents is not always reliable, so they can receive a reliable knowledge in school, and an extra knowledge from parents)

Thank you

I think you need to say more if you want to be clear. Right now, your thought is incomplete.

The knowledge that they receive from their parents can build on what they learn in school.

Or, to completely rewrite the sentence: Parents can give us knowledge greater than the facts we learn in school.

I hope this helps.

You can write something like -- parents pass down their knowledge to kids, though education should not be limited only to this. Anyways, it feels like your sentence is incomplete -- add one clause to explain why it should be extra. And if you need help with editing, you can get tool from this official website or this official website .

Good luck!