The answer is actually simple:
<%= select_tag "instructor", options_from_collection_for_select(@instructors, "id", "full_name"), :include_blank => true, :class => "example_class" %>
Will produce:
<select id="example_select" name="example_select" class="example_class">
<option value></option>
<option value="1">Example option 1</option>
<option value="2">Example option 2</option>
</select>
Thanks Jesse Goodfellow