really interesting question! We exposed my DS5 to print as early as I can remember by just making it available - we never "taught" him we just answered his questions or played silly word/letter/sound games while driving in the car.... we knew he was visual from pretty early on and I labeled everything in the house...it looked pretty silly to visitors that we had labels on everything from the sink to the front door but he loved it and he could read environmental print by 2 years old, was reading words out loud to us that he saw everywhere when he was 3 and was reading from books by about 3.5. We question the same thing...he seemed to learn by osmosis as we like to joke - he was a sponge and just took everything in and next thing we knew he knew all his letters and sounds and figured out how to read all on his own. He can hear/see a word one time and he knows it. I was worried that he hadn't learned phonetically but he seems to be doing fine...he does the same thing...we will be reading along and I will see a word coming up that i am convinced he doesn't know and whamo he surprises me by reading it with no issue. I was also a very early reader and my dad said the same thing - it just was :-)