I have started a discussion about solutions for this issue here:
I see three general solutions to this. Hopefully #3 could be a solution that combines the first two ideas.
1. Don't allow students to edit or delete Q&A posts.
Solves the problem but students might be surprised by this since it is different than other forums. Students may legitimately be using the editing time to find last second errors.
2. Don't allow students to see other's posts until they are no longer able to edit or delete their post.
The plus side is that the logic for whether the student can edit their own post is already there. The downside is that it would slow down the Q&A forum process, especially in the cases where students were to reply to other student's answers.
3. Use Solution 2, but add a student option that ends the editing/deleting period for the post. This could be when the post is created similar to where the 'Mail now' option for teachers is and/or after posting next to the edit and delete options for a post.