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| %>

    <th>Parcial 1</th>
    <th>Parcial 2</th>

  <% for evaluation in @evaluations %>
      <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>
  <% end %>

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

Thanks you much for your help.