= simple_form_for @user do |f|
  = f.input :name
  = f.input :email, label: "E-mail"
  = f.association :subscriptions, collection: @user.subscriptions,
    as: :check_boxes, value_method: :active, checked: lambda { |subscription| subscription.active? }

  = f.button :submit, "Save"

= simple_form_for @user do |f|
  = f.input :name
  = f.input :email, label: "E-mail"
  - f.simple_fields_for :publications do |subscription|
    # Here you have all simple_form methods available
    = subscription.check_box :active

  = f.button :submit, "Save"

attr_accessible :subscriptions_attributes