I do child care in my home and have been successful with the dot to dot method and I usually start with the 3 year olds.
Start with a whole line of dot to dot A's-B's and C's and leave a space under each letter. let the child do the letters by connecting the dots and on the next line try the letter on their own by looking at the dot to dot letter they completed. I praise them for every attempt. I start with 10 minute sessions and expand the time as the child gets better. I have a 5 year old in my care now that can do all ABC's, address, phone number, his whole name and birth date. Which makes me so very happy when they can do things for themselves.
Good luck. B.