class Foo < ActiveRecord::Base
  before_validation :check

  def check
    puts "i'm being checked in foo's before validation"
  end
end

class Bar < Foo
  before_validation :check

  def check
    puts "i'm being checked in bar's before validation"
  end
end

>> Foo.new.valid?
i'm being checked in foo's before validation
=> true
>> Bar.new.valid?
i'm being checked in bar's before validation
i'm being checked in bar's before validation
=> true