school.rb

class School
  attr_accessor :roster

  def initialize(school)
    @roster = {}
  end

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

  def grade(num)
    @roster[num]
  end

  def sort
    @roster.each {|k,v| @roster[k] = @roster[k].sort}
    @roster
  end

end