Why I don't use class variables in Ruby (or try not to)

class_instance_vars.rb

class Person
  @name = nil

  # class-level reader
  # cattr_accessor is rails-specific not ruby, and uses class vbles so ...
  # may be done like this too:
  #
  #   class << self
  #     attr_reader :name
  #   end
  #
  def self.name
    @name
  end
end

class A < Person
  @name = "John"
end

class B < Person
  @name = "Doe"
end

puts A.name
# => John
puts B.name
# => Doe
puts Person.name
# => nil

# class instance variables are enclosed inside the scope of their own class
@name = "Something"

puts A.name
# => John
puts B.name
# => Doe
puts Person.name
# => nil

class_vars.rb

class Person
  @@name = nil

  # class-level reader (cattr_accessor is rails-specific, not ruby)
  def self.name
    @@name
  end
end

class A < Person
  @@name = "John"
end

class B < Person
  @@name = "Doe"
end

puts A.name
# => Doe
puts B.name
# => Doe
puts Person.name
# => Doe

# also, class variables may be modified globally
@@name = "Something"

puts A.name
# => Something
puts B.name
# => Something
puts Person.name
# => Something

attr_acessor is not a rails specific method. attr_accessible is. Also on your getter method on the first example, self.name is redundant:

def name
@name
end