By special request: in the last week I’ve explained this to  administrators  from two separate schools just starting out with Moodle this term. While there are ways to enroll your students into groups (ie, classes/sets, whatever you wish to call them) it’s rather nice for them and you if you get them to do the work. You do this by clever use of the group enrolment key – click on the image for a youtube video. Basically…

1. you set your course up
2. in course settings you ensure your course is enrollable and you have groups set (visible or separate) and that guests are not allowed in;
3. you set a course enrolment key – it doesn’t actually matter what, as it won’t be needed. It’s to keep other people out.
4. you then go to groups in the course admin block and click on Create group
5. Name your group – the name of your set/class
6. set an enrolment key for that particular group. You could use the set’s name so they only have to type in the name of their set – but you are relying on them knowing which set they are in and how to spell it. (But that would be a problem with any password)
7. Save and repeat for as many groups as you have
8. When you next see your class, tell them to log in as usual to Moodle, go to All courses and find your course.
9. When prompted for an enrolment key they need to type in their group key – the one you set in 6 above.
10. And they are not only enrolled in the course but neatly put into groups for your gradebook !

ADDENDUM: With thanks to UK Moodler and teacher Dan Leighton: if your groups(classes/sets) are in years, such as 8A, 8L etc and you set the password as the group name, then set the course password to begin with the year also – in this case, 8. This is because if students forget their group enrolment key , Moodle prompts them with the course password – so if this does not begin with their year, they will just get confused, and we wouldn’t want that, would we?