associations...

You can always add an assignment table like this:

class Teacher < ActiveRecord::Base
  belongs_to :location
  has_many :qualifications

  # location_id
end

class Location < ActiveRecord::Base
  has_many :teachers
end

class Qualification < ActiveRecord::Base
  belongs_to :quality
  belongs_to :user

  # teacher_id, quality_id
end

class Quality < ActiveRecord::Base
  has_many :qualifications
end

User.location # New York
User.qualifications # List of qualities