lortest.rb

class School 
  attr_reader :roster,:school

  def initialize(school)
    @school = school
    @roster = {}
  end

  def roster
    @roster
  end

  def add_student(name,grade)
    self.roster[grade] ||= []
    self.roster[grade] << name
  end

  def grade(grade)
    self.roster[grade]
  end

  def sort
    self.roster.each { |k,v| v.sort! }
    Hash[self.roster.sort_by {|k, v| k}]
  end

end