Hi K.,
I'm a mom of two girls, college and high school aged, and I have " been there- done that". I think your discipline is too sophisticated for the three-year-old developmental mind. At three children are "king of the universe" and they are only beginning to learn cause and effect and empathy. Important lessons for socialization.
When my kids began to do the hitting and biting thing.(they didn't scratch, but it's all the same) .. It was usually because they were over-stimulated somehow.
I suggest addressing the behavior immediately, right on the spot wherever you are. The consequences should be plainly linked to the action. Other wise a child that age, can't associate their actions with the results... If you do it consistently I believe that he behaviors should stop very quickly.
As soon as he scratches someone, get eye to eye, holding your child's hands to prevent further scratching, and in a FiRM voice with a disapproving face, simply say :we do NOT scratch people, it Hurts them" and then pick him up and remove him from the area. Do not use the sing-song voice or hold him in hugs, it sends mixed messages .
If he scratches you are your husband, you should "yelp" in pain, to make it clear that he is causing something "bad" to happen too you. He will cry.. But that's OK. He SHOULD feel uncomfortable when he hurts people.
I would usually put my kids in their rooms,..I'd leave the restaurant in the middle of the meal if I had to, I'd apologize to friends and end a play date on the spot, etc. Immediate response to unacceptable behavior. I only had to do that a few times.
Yes my daughter would scream and I'd feel guilty and like a horrible mom, and second-guess myself... Bit the behavior lessened immediately and with warnings,disappeared in very little time.
I always told my kids ahead of time what I expected, and the consequences. "If you scratch anyone at the playground, we will leave".
In my case I only had to leave a park playground twice, and the older sister hated it. But Like I said, only twice.
If I noticed her getting frustrated I'd intervene if I could, to prevent the behaviou\r, and I'd remind her "no biting" in a firm voice..
I think charts and, and consequences that don't directly relate to the behavior ( like taking away a toy for scratching you) and other intellectual approaches are more effective in kids older than four.
I hope you can teach him empathy and cause and effect. It helped my girls grow into wonderful young women.
Best of luck, Val
PS: I read some of the other responses, and (no flame intended) .. Do NOT scratch him in back.. You will only teach him that you, some one who is his whole world,is willing to hurt him!
You are trying to teach him NOT to do that, so it's a mixed message to do it yourself! "Two wrongs do not make a right"... An important lesson for life.