My mother was talking to her boyfriend Jimmy one day and I over-heard them talking. He had no idea what the difference was between to, two, and too when written. I remember learning this shortly after learning how to read, and I don't think it's that difficult. She explained it decently well but I could tell some of it he just didn't get. I then said "The two of them went to the beach too.". Both of them thought it was funny.