public interface ISyncer
{
    // Read input and synchronize destination, return error message if any
    string Sync();
}

public class StudentSyncer : ISyncer
{
    // simple XML reader, reads XML file into a list of List<XMLStudent>
    private XMLStudentReader _reader;

    public StudentSyncer(string file)
    {
        _reader = new XMLStudentReader(file);
    }

    public string Sync()
    {
        // read the input
        List<XMLStudent> source = _reader.ReadAll();

        // using automapper map to domain object
        List<Student> dbStudent = Mapper.Map<List<XMLStudent>, List<Student>>(source);
        dbStudent.ForEach(s => s.IsCurrent = true);                // set IsCurrent

        using (var context = new DbContext())
        {
            UnitOfWork uow = new UnitOfWork(context);
            // set the existing records to not current
            var curSet = uow.Student.FindByTrackingChanges(s => s.IsCurrent == true).ToList();
            curSet.ForEach(s => s.IsCurrent = false);

            uow.Student.AddRange(dbStudent);
            uow.SaveChanges();
        }
        return "";  // no error
    }
}

public void DoSync()
{
    foreach (string file in Directory.EnumerateFiles(@"C:\Source", "*.xml"))
    {
        // use syncer factory to initialize the correct instance of syncer based on input file name
        ISyncer syncer = _syncerFactory.CreateInstance(file);

        // do the synchronization task
        syncer.Sync();

        // Move file to processed folder
        MoveFile(@"C:Destination");
    }
}

abstract class SyncerBase : ISyncer
{
    sealed List<T> Map(List source, List target)
    {
        // Mapping magic here
    }

    sealed SaveToDB(List dataToSave, params ...)
    {
        // Your database access here
    }
}

class StundentSyncer : SyncerBase
{
    // Constructor as in your code
    void Sync(string file)
    {
        var XMLstudents = _reader.ReadAll();
        var students = Map(XMLstudents); // calling base class here!
        // Manipulate student list here as needed
       SaveToDB (students, database params here) // base class here, too
    }
}