Check out the [AnythingSlider FAQ](https://github.com/CSS-Tricks/AnythingSlider/wiki/FAQ#wiki-fouc) page. There are two methods shown there, the first and best one, shows how to add the overflow properties. But if you are using the latest version of AnythingSlider, this should already be contained within the anythingslider.css file.
Update: Ahh, I see you’re using the WordPress plugin. It looks like you can’t really use an ID the anythingslider.css because it changes with every reload. Maybe try changing [line 12](http://classroommatters.com/wordpress/wp-content/plugins/anythingslider-for-wordpress/css/anythingslider.css?ver=3.4.1) from `.slider` to `#anythingslider ul` since AnythingSlider is wrapped in a div with an id of “anythingslider”.