Joseph Rézeau

1- Are you quite sure that the students have reached the end of the lesson? When a lesson is not properly finished by the students, it cannot be graded.
2- Does the Lesson have a grade (see screenshot below)?
3- Which version of Moodle are you using?
4- Is this a problem that has developed recently? or did you have lessons which were recorded correctly previously?
Joseph

Hi Nick,
I don't see how your post is related to this Questionnaire module forum.
Joseph

Hi Nick,
Did you upgrade your Moodle version (from 1.9.x to 1.9.5) ? and then upgrade your Questionnaire module? How exactly did you "upgrade" your Questionnaire module? Do you use CVS?
You should have backed-up your questionnaires before the upgrade.
The blank screen is a sure sign of a problem somewhere. In Admin mode, turn on the debugging and see whether you get PHP error notices in the "blank page".
Joseph

Maybe you could try the "Outcomes" option, which your admin must set in your moodle site General settings:

Enable outcomes
Default: No
Support for Outcomes (also known as Competencies, Goals, Standards or Criteria) means that we can grade things using one or more scales that are tied to outcome statements. Enabling outcomes makes such special grading possible throughout the site.

It's difficult to know the reason why you are having this problem. Is this a "normal", private questionnaire in one course only, or a questionnaire based on a public one from another course on your moodle site?

If you select Members of All groups or People not in a group, what results do you see? Is it the same as All participants?

If you export the data in the Download as text tab for all participants, do you get anything in the Groups column?

In other activities in that course, are the groups working as expected?

Does this happen only with this one questionnaire? Have you tried another questionnaire in the same course?

Please experiment and come back with more details.

Joseph