Hi, thank you for contacting JustAnswer.com. My name is Russell. I will do my best to provide the right answer to your question.
Your son may not have updated the drivers properly. Canon has indeed released drivers, and software, for your current version of MAC OS X (El Capitan or version 10.11).
Would you be willing to follow my instructions as to properly doing the task of substituting your currently installed drivers for the scanner, for unquestionably updated and appropriate drivers? this is not a process that can necessarily be done properly in a casual fashion, in a case like yours where an update to the MAC OS operating system level has caused disruption of device function. Such a case deserves exact and detailed instructions, which I will give you, if you will follow them.
Let me know, please. Thanks.