Javascript event on form add fields

I've got a rails app using bootstrap with a form page that has the option to add additional form fields. The tutorial from this Railscast episode heavily influenced this form page add fields feature. I have a need to watch the add fields so that I can hide a warning panel in the new well created. Here is the code that will not work:

  $('#classifications_forms').on 'change', (event) ->
     container = $('.classifications_form').last()
     $('#premium-divide', container).hide()

I have tried an on click event for the add fields button, but it's late in the event watching as it will not hide the panel. If I hit the button a second time, it will hide the panel on the previously created well, so I know the code was working to hide the panel. My thinking is to hide the panel on the last well created, and I thought that a change on #classifications_forms would give me the event needed to hide the last well, but I guess its missing something on the event. What is missing above?