Hi MARIA_186,
Thank you for your further reply. I’m glad to help you further.
Based on your description, I’m afraid and sorry to say it isn’t correct as the Teacher will only see the old one as you need to Undo turn in first, then click Turn in again to trigger the resubmit of your Word document, otherwise your teacher will not see your new edits in this Word document. For your reference: Turn in an assignment in Microsoft Teams - Microsoft Support [6440-ab76-e53-505d].

The reason why you can edit the Word document by clicking the Edit button is because your teacher set the assignment into Students edit their own copy. For your reference: Create an assignment in Microsoft Teams - Microsoft Support [ff99-fb4b-9d1-bfa2].

However, your new edits won’t be viewed for your teacher unless you follow the steps above to trigger the resubmit as it doesn’t have synchronization between your edits and your submitted assignment.
If you think this by design scenario is inconvenient, Personally, I’m also totally understanding the convenience of simply editing the assignment without resubmitting to let teacher view the modification. Due to this situation, I also suggest you can go to this link: Microsoft Teams · Community to go to our Feedback community and send your feedback and requirements. Our product team is in charge of the site, and they constantly check customer reviews and feedback, and a lot of the features are developed and improved based on customer feedback.
Appreciate again for your patience and understanding.
I wish you keep safe and having a great day as well.
Sincerely,
Harry | Microsoft Community Moderator