If the student is currently enrolled in an Active class, their Enroll Type = Enrolled and Class(es) appear in the Current Schedules section of the student's Schedules tab.
The student did not complete the class. The student was dropped before the class was completed using the Drop link. This is considered a 'true drop' and will appear on the Drop History Report. If a student is dropped from a class, the class appears in the Past Enrollment section of the student Schedules tab. Note: It's important to archive classes (rather than drop students from class after it ends) so that reports will only display 'true' drops. See Archive Classes.
A student is considered transferred when they have been moved from one class to another. This creates a Past Schedule record, but this is not considered a drop. It is treated as a Transfer and does not negatively reflect on the school / class / teacher and is excluded form the drop reports.
In the Past Enrollment section (Student Classes tab), the Comp? column indicates whether the student completed the class (Yes) or did not complete the class (No.)