When the money is paid into court (by the offender) a cheque will be sent to your son. If the court gave the offender time to pay (i.e. in instalments) then a separate cheque will be sent every time the court receives an instalment.
That's how I received compensation after a break-in at my former home. I'm assuming that the same will apply in your son's case.
If the compensation is from the Criminal Compensation Board it will come by cheque........if it is compensation from the person who assaulted him I assume as Buenchico said.
My late mother-in-law was injured during an armed robbery....they never caught the perpetrators but she got a few thousand compensation for her injuries.