4yr old teasing dog

My 4yr old only child son has been relentlessly teasing our family dog. I know he is lonely and we are looking into getting him into a social program before preschool begins next year. He does not in any way hurt and harm her but he follows her too closely, tries to get reactions out of her, scares her and traps her. She is adopted from an abusive home, we do not know what happened to her but she was a mess when we rescued her. Is there anything I can do to get through to my child that she is a special dog and should not be teased. We have tried yelling, time outs, separating him from the dog, taking away toys. Nothing works. He thinks she is his friend but I can't seem to make him understand that that is NOT how we treat animals or friends. Thank you for any advice you may have.

[Encephalomalcia]

Give him a real good talking to.  Tell him this is not how we treat animals.  We need to respect animals.  Make the talk lengthy so you get through to him.  Make direct eye contact and tell him that this teasing is going to stop right now.  Be firm, direct, to the point, and repeat, repeat, and repeat.  Make him repeat it back to you.  If he continues, put him in time-out until he starts feeling bad for what he did.  It took my step-daughter once 30 min. in time-out before she started feeling bad.  She hit her sister over the head with a guitar and she thought it was funny.  At first, she made faces and laughed in time-out until she realized that she was going to be there a long time.  She had no idea how long she was going to be in time-out.  She never hit any of her sister over the head with anything again.  Lessoned learned.