gistfile1.txt

class School

  attr_accessor :db

  def initialize
    self.db = Hash.new([])
  end

  def add student, grade
    db[grade] << student
  end

  def grade grade
    db[grade]
  end

  def sort
    db.keys.sort.reduce({}) do |new_db, key|
      new_db[key] = db[key].sort
      new_db
    end
  end
end

gistfile2.txt

[3] pry(#<SchoolTest>)> school.add 'Aimee', 2
=> ["Aimee"]
[4] pry(#<SchoolTest>)> school
=> #<School:0x007fd34206bdb0 @db={}>
[5] pry(#<SchoolTest>)> school.db
=> {}