好.我想，我可以通过年级来获得学生的名字，而不是通过学生来获得年级的名字，所以我做到了

Ok. I figured that instead of getting the name of the Grade throught Students, i can get the student through grades, so I did

<% aula.grades.each do |grade| %>
  <%= link_to grade.student.name, student %>-<%= grade.name %>
<% end %>

现在它好起来了.