Why does Post threshold for blocking still not stop students from exceeding the threshold?
Once the ‘Post threshold for blocking’ is armed and set in the forum activity instance, it is actually the mod/forum:throttlingapplies capability that enforces it. By default, this is set to ‘Not set’ in the student role. Either set this to ‘Allow’ for the student role in system, or use a override on the forum activity instance this applies to. While one forum can have one limit, it can be applied to one user and not another by using the roles system. For more information see MDL 10720 or discussion here.