course.rb

class Course

  attr_accessor :title, :location
  def initialize(params = {}); end
  def add_teacher(teacher); end
  def add_student(student); end
  def for_each_student; end

  private
  attr_accessor :teachers, :students

end

person.rb

class Person
  attr_accessor :name, :age

  def initialize(params = {}); end
end

student.rb

class Student < Person
  protected
  attr_accessor :gpa
  def initialize(params = {}); end
  def add_course(course); end
  def complete_course(course, gpa); end

  private
  attr_accessor :courses, :grades
  def calculate_gpa; end
end

teacher.rb

class Teacher  < Person
  attr_accessor :description
  def initialize(params={}); end
  def add_course(course); end

  private
  attr_accessor :courses
end