Do you call it Solfège or Solfeggio?

Unless you are a music teacher, you probably do not know what is solfège, or solfeggio.  I did not know what it was, but I am reliably informed that if you want to progress with your piano playing, you need to learn it.  The system has been in use as a pedagogical aid since it was developed by Guido D'Arrezzo in the eleventh century.

I have two piano playing sons; Ted, aged 12, and Monty, aged 9.  Monty, as you will know, has ASD.

Who do you think is going to be the first to learn solfège?   It’s going to be Monty.

Ted is not amused.