form.erb

<%= form_for(@spek) do |f| %>
  <div class="field">
    <%= f.label :klass_id %><br>
    <%= f.collection_select :klass_id, Klass.order(:name), :id, :name, include_blank: true %>
  </div>
  <div class="field">
    <%= f.label :name %><br>
    <%= f.text_field :name %>
  </div>
  <div class="actions">
    <%= f.submit %>
  </div>
<% end %>

form.haml

= form_for @spek, :html => {:class => 'nice custom'} do |f|
  .row
    .large-12.columns
      = f.label :klass_id, 'Class'
      = f.collection_select :klass_id, Klass.order(:name), :id, :name, prompt: 'Select a Class'
  .row
    .large-12.columns
      = f.text_field :name
  .row
    .large-12.columns
      = f.submit 'Create Specialization'