app/views/teachers/new.html.erb
<h1>Add a new teacher to <%= @organization.name %></h1>
<%= form_tag :organization_teachers do %>
<%= render 'shared/error_messages', target: @teachership %>
<div class="field">
<%= label_tag :username %>
<%= text_field_tag :username %>
</div>
<div class="actions">
<%= submit_tag 'Add a new teacher', class: 'btn btn-info' %>
</div>
<% end %>