I'm triying grouping and dont work like say here: http://docs.moodle.org/en/Groups_versus_groupings
I make 3 groups (A, B and C) and 1 grouping (G1, with group A and B). Add a 1 student into group A and another student in group C. Add a activity choice into course, and configure it selecting in Grouping option G1, and mark "Available for group members only". Login as student in group C, I can see, enter and make a choice in the activity that configure only for grouping G1, and can see the choice was make the student in group A.
Similar to in a forum with the same configuration (Grouping G1, and "Available for group members only"). Student in group A can post in that forum; student in group C can enter the forum and read the post of student A, only one restriction, student in group C cant make a post or response in that forum.