Step 8 - Basic Backend - checkall not working

[pkdbaxter]

When in the backend, clicking on the checkbox to 'select all' does nothing.
Reviewing the source of the rendered page it appears that the core.js is not being included which is where the checkAll function resides.
I added the following to the top of the default.php file and it now seems to work as expected:
JHtml::_('behavior.multiselect');
As I am totally new to Joomla and php, I am just taking a shot in the dark here. It would much appreciated if someone could provide feedback

Thanks!
Peter