What helped DD, honestly, was a V-tech laptop with ABC games. They teach the kid upper and lower case. I also got DD one of those phonic fridge magnet things that sings "F, F, the F says ffff" - it only does uppercase, but that's a start, right?
Chicka Chicka Boom Boom is a great letter book. We have also used Starfall. There's enough free content to get you going.
We also do the alphabet on the road game, or play other letter games. Same way we did with colors, numbers, objects.
A walk can be a great learning moment. "Son, what is THAT?" "A stop sign, Mommy." "Are you sure? What shape is a stop sign?" "An octagon" "What color is a stop sign?" "Red" "What does a stop sign SAY?" "Stop!" "S-T-O-P, stop. You're right. How very smart of you. Do you see any more?"
I will also say that DD was tested for various things in Sept. She is also an August baby and they just wanted her to know how to write 2 letters from her name. If time goes on and you feel he's not progressing, then talk to your school district about further testing to see if there's another issue like dyslexia.