I can give you a teacher perspective on this. I taught kindergarten several years. *Most* teachers are more than happy to talk to you, provided you schedule a conference. Don't just try to talk about it after school or when you drop off. We have things to do, meetings, planning, prep, etc.
Come to the conference prepared. Make a list of what you want to be sure to say. Don't present a problem without a solution. So, if the problem is the flip-flopping between levels, you may ask that he have just the level he is on. However, I imagine the lower levels reappearing is to help with fluency or just to make it more enjoyable for him if the J level is a little too frustrating for whatever reason. If they are doing guided reading, truly, they must have a guided reading library full of books on each level. They aren't all chapter books. There are lots of leveled books on nonfiction topics too! You may even ask her to bring some samples of them to see if there are some of the other types of genres of guided reading books he may do better with. For your own personal information, I think Lakeshore Learning sells some of the best sets on the market. I have sets A-E for dd4. Their non-fiction is great!
Other ideas...what is he being asked to do with the books? Is he filling out a summary sheet for them? Answering comp questions? Practicing for fluency? AR tests? (Book Adventure is a similar program you can do at home.)
Oh! And be on time, leave on time (so she isn't rushing to pick up the class from gym or whatnot), and try to find something nice to say at some point.
