T.F.
I always wrote a thank you note, no excuses. Most of the time I'd have my daughter draw if she couldn't write her name. By K she was writing her name, not perfectly, but she always had a part in "signing the card".
She is now 15 and the thank you note is in her brain. Nothing is used until a note is sent out and if it is more than 3 days it is LATE. Just my opinion because i am a stickler for Thank you notes and RSVP's.
Good for you for sending a note. I believe teaching proper manners is critical. So many people just throw manners out the window now and it is sad that so many children will not learn proper manners.