I think you'd get the results you want if you wrap the checkboxes iterator in a fields_for :checked_boxes
tag - or at least get you close to the results you want.
<%= form_for(:object, :url => { :action => 'create', :id => params[:id]}) do |f| %>
<p>Field_a: <%= f.text_field(:field_a) %></p>
<p>Field_b: <%= f.text_field(:field_b) %></p>
<p>Field_c: <%= f.text_field(:field_c) %></p>
<p>Check boxes:</p>
<%= f.fields_for :checked_boxes do |cb| %>
<% check_box_choices_object_array.each do |s| %>
<%= cb.check_box(s.name, 1, false) %>
<%= .name %><br />
<% end %>
<% end %>
<%= submit_tag("Create") %>
<% end %>