Wordpress dropdown menus

I would like to create dropdown menus and thought I knew how to do it, just following this tutorial: http://www.ostraining.com/blog/wordpress/dropdown-menus-in-wordpress/ However, when I do it and then scroll over the menu that is supposed to be drop down, nothing happens. The child page is there if I go directly to the link, but it doesn't appear in the menu. What am I doing wrong?