app/views/grouped_progress_entries/_new_participant.html.erb
<div class="hidden_participant">
<%= select_tag("student_intervention[participant_user_ids][]", options_for_select(users), :disabled => 'disabled') %>
<%= link_to "X", "#", :class => 'cancel_link', :data => {:remove_up => 'div'} %>
</div>