Okay ... now I understand. I see no issue with approaching the teacher. Following the lines of the best way not to offend is to compliment: I would explain the enjoyment your son has and how he is asking for more and then offer up the suggestions as you described.
My daughter is in a Spanish Immersion school and brought home a library book the other day. I have no ability when it comes to reading Spanish so it was fun for both of us. :P BUT getting through the book with her helping me along the way made me realize that she is close to reading Spanish. She is able to read in English and was reading the English part to me while I was working on the Spanish with my IPad and translator.... yeah, I'm that bad! And when I had it translated we would repeat the words and follow the text until we had it down. I'm thinking about approaching her Teacher about working on her reading in Spanish. I suspect all she needs in some one on one time with her and understanding of putting the sounds together.
