ADD is potentially the explanation, NOT an excuse.
No disrespect towards your parents, but fighting ignorance is an uphill battle. Arm yourself appropriately. I know when I first discussed the matter with my parents it was a nightmare. They were “stick their head in the sand” kind of people 
If you do open a dialog with your parents, you might want to start by saying something like “you know, I’ve done a lot of reading and the medical professionals are quite clear that ADD has to do with the way a brain is ‘wired’ inside — it is not caused by weak morals or bad parenting which are old wives tales still being circulated today”. Science has also found genetic markers in DNA that have been CONCLUSIVELY linked to ADD which is another important point you can make.
It could be your parents will be defensive if they’ve heard the old wive’s tales themselves. In my case, BOTH my parents share many of the traits I have. They were, in part, being defensive because my bringing the subject up, and information into their household, meant they had to face the fact they too might have this issue.
It also might help to identify some very successful people who have coped with AND EXCELLED BECAUSE OF their adhd. People like Richard Branson, Mark Twain, John F Kennedy, Ronald Reagan, Princess Diana, Buzz Aldrin, Harrison Ford, etc…..
Read about it some more, relax and when the time is right start the dialog with them. It may also help to tackle the issue with one of them at a time. I also think the suggestion to watch the video alongside them is a good one.
Cheers!
REPORT ABUSE