There are four requirements that must be met in order to link sections.
1.The courses must be the same.
2. The rosters must be unique (the same student can't be in both sections)
3. The marking periods must be the same.
4. The admins must be the same.
If you attempt to link, and the sections are grayed out, you can hover your mouse over the course and see what is causing the linking issue. (see image below)
We've noticed that if students have changed sections, they might still be in the original course in Schoology. This will prevent the courses from linking. If this happens teachers will need to check their rosters and manually unenroll the student from the course they should not be in. Then they should be able to link the courses.
***Remember that linking and unlinking while a course is in progress can cause grades, assignments, materials to be lost so please back up your data before trying this.***