ActiveRecord can't deserialize hashes with range keys

AR seems able to serialize just about anything you give it, but it throws an error when given a hash that contains a ruby range as one of its keys.

class Student < ActiveRecord::Base
  validates_presence_of :age
  validates_numericality_of :age, :greater_than_or_equal_to => 0, :only_integer => true

  serialize :schools, Hash

  def school
    schools.detect{|k,v| k === age }.try(:last)
  end
end

student = Student.create(:schools => {(5..10) => :elementary, (11..13) => :middle, (14..17) => :high}, :age => 6)

The creation works for me but when AR tries to deserialize the "schools" hash, I get the following error:

ActiveRecord::SerializationTypeMismatch: schools was supposed to be a Hash, but was a String