has many through + additional value

My Code:

models:

has_many :skill_users, :dependent => :destroy
has_many :users, :through => :skill_users

has_many :skill_users, :dependent => :destroy
has_many :skills, :through => :skill_users

belongs_to :user
belongs_to :skill

skilluser table

-id
-skill_id
-user_id
-rating

form:

simple_form_for @user ....
Skill.all.each do |skill|
hidden_field_tag "user[skill_ids][]"
check_box_tag "user[skill_ids][]", skill.id, @user.skills.include?(skill),
{ :id => "user_skills_ids_"+ skill.id.to_s}
skill.name

Rails 3.2
How do I manage to get the rating attribute attached to each checkbox and stored in the db? I can't find a solution Googling.

Would be great to get some help…

tried this:

hidden_field_tag "skill_users[][skill_id]", skill.id
text_field_tag "skill_users[][rating]"

but no success.

Thanks

Werner