## school_classes_helper.rb

  def add_classes_link(name)
    link_to_function(name, nil, :id => "btn_add_class") do |page|
	  page << "counter = 0"
	  page.select('tr.school_class').each do |c|
	    page << "counter += 1"
	  end
	  page << "if(counter < 9) {"
	    page.insert_html :bottom, :secTable, :partial => 'school_class', :object => SchoolClass.new
		page << "if(counter==8) {"
		  page.hide "btn_add_class"
		page << "}"
	  page << "}"
    end
  end

## _school_class.html.erb

...

<%= link_to_function( image_tag('buttons/btn_dest.png', :border => '0'), :id => "btn_rem" ) { |page|
	    page << "$(this).up('.school_class').remove()"
	    page << "counter = 0"
	    page.select('tr.school_class').each { |c|
	      page << "counter += 1"
	    }
	    page << "if(counter < 9) {"
		  page.show "btn_add_class"
		page << "}"
	  } %>

...