Here are some ideas for how to achieve a working StudentDirectory using YAML

gistfile1.txt

# Let's make @directory an array, rather than a String
@directory = []

# Pull in existing people from a YAML file
@directory += YAML.load_documents(File.open('student_directory.yml'))

# Save people to a YAML file
File.open('student_directory.yml', 'a') { |f|
  @directory.compact.each do |person|
    f.write(person.to_yaml)
  end   
}