Help with form_for

I have this rhtml, that generate a table with the object @evaluations filled it before. The problem is that i need to get those text_field with the data loaded, but instead it' filled all text_field whit the last @evaluation. What i am doing wrong?

<% form_for( @evaluations ) do |f| %>

  <table>   <tr>     <th>Student</th>     <th>Commission</th>     <th>Id</th>     <th>Parcial 1</th>     <th>Parcial 2</th>     <th>Final</th>   </tr>

  <% for evaluation in @evaluations %>     <%= evaluation.id%>     <tr>       <td><%=h evaluation.student.fistName %></td>       <td><%=h evaluation.commission.code %></td>

      <td><%=f.text_field(:id, :size => 2) %></td>       <td><%=f.text_field(:first_evaluation, :size => 2) %></td>       <td><%=f.text_field(:second_evaluation, :size => 2) %></td>       <td><%=f.text_field(:final_evaluation, :size => 2) %></td>

      <td><%= link_to 'Show', evaluation %></td>       <td><%= link_to 'Edit', edit_evaluation_path(evaluation) %></td>       <td><%= link_to 'Destroy', evaluation, :confirm => 'Are you sure?', :method => :delete %></td>     </tr>   <% end %>   </table>

  <p>     <%= f.submit "Update" %>   </p> <% end %>

Thanks you much for your help.