gistfile1.rb

class ParentFoo
  def foo
    _foo
  end

  private

  def _foo
    puts "parent private foo"
  end
end

class ChildFoo < ParentFoo
  def foo
    super
  end

  private

  def _foo
    puts "child private foo"
  end
end

ChildFoo.new.foo
#=> child private foo
#=> nil