How to set defaults for articles created on frontend

[divio]

I have two groups, student and teacher. ACL is so set that
1. public can see only public (article)
2. student can see only public and student
3. teacher can see all
I have a menu (create article) for teachers to create articles at frontend so that only students and teachers can read. I had read and search a lot to get the above done.

However, QUESTION, the default access level of those articles created is "public". I hope I can set its default to student.

I know it can be teacher's responsibility to set it right when they create article, but ...
I know I can use "menu" to block public out from reaching the article in normal way.
But I still hope I can do the housekeeping work properly. Can it be done?
Thanks,