One field for each one category - SOLVED -

Have you considered using an e-learning platform like moodle?

Regards

To identify a student's note I wrote the student's name on the label of the field "select".

You said you have name of student in a field.
Also the notes you display them in category view or item view , or you use both?

Regards

Yes, I started with moodle. But moodle is a platform designed for educational content to teach.
My content is not educational. My content is administrative.
Moodle contains a module called "mentees" to prepare information for parents but it is very restricted.
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I put in the label of the select field the name of the student.
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For a student to see the notes I've created a menu.
In this menu there are items such category "flexicontent": the sub-sub-category with the student's name.

So each student note is flexicontent item located a student specific category?

Students are sub-categories flexicontent, this I have it clear: Sub-categories.
What I do not understand is what you call the "flexicontent item". I call "item" to the components of a menu.
Anyway, the note of each student is related to his category. For a student to see your note he has a menu item type "flexicontent-category" which display the contents of the sub-category that bears his name.

Then you can go to the category and change its permission to exclude all students but the one should see it ...