...
<Window.Resources>
  <CollectionViewSource x:Key="studentsViewSource" d:DesignSource="{d:DesignInstance my:Students, CreateList=True}" />
  <CollectionViewSource x:Key="groupsViewSource" d:DesignSource="{d:DesignInstance my:Groups, CreateList=True}" />
</Window.Resources>
...
<Grid DataContext="{StaticResource studentsViewSource}">
  <ListView Height="200" ItemsSource="{Binding}" Margin="0,0,0,61" Name="studentsListView" SelectionMode="Single">
...
    <GridViewColumn x:Name="groupIDColumn" Header="Группа" Width="100">
                        <GridViewColumn.CellTemplate>
                            <DataTemplate>
                                <ComboBox Margin="-6,-1"
                                          SelectedValuePath="GroupID"
                                          SelectedValue="{Binding Path=GroupID}"
                                          ItemsSource="{Binding Source={StaticResource groupsViewSource}}"
                                          IsSynchronizedWithCurrentItem="False"
                                          DisplayMemberPath="Name">
                                </ComboBox>
                            </DataTemplate>
                        </GridViewColumn.CellTemplate>
    </GridViewColumn>
...