Depending on how the individual course pages are configured, LabTutor 4 will import a student list for all current courses or for a specific course. To populate the Import students into course: drop down menu with all of the courses and upload student lists to specific courses, you will need to restrict access to each course. To accomplish this, go do the edit course tab for each course and check the Restrict access to this course check box (see screen shot below).
The Import students into course: drop down menu will then be populated with all the courses currently defined in LabTutor Server. To allow all students on the import list access to all courses and experiments, simply uncheck the Restrict access to this course check box for each course.
Note: The ability to restrict students to specific courses is only available in LabTutor 4.5 and later.