Hi and Welcome!
I, too, wouldn't worry much at this point. It will come for him. It is not unheard of, especially for a perfectionist, to not want to walk/talk/read until they feel completely competent. This may be the case with your DS. Also, your DS may simply have the perception that school is supposed to be only fun, not work. He is 6, afterall! And even if he's not yet producing high-level work, his brain IS working at a higher level than most. Now, if you are worried that there is some reason other than normal development that is keeping him from working at a higher level, then keep it in the back of your mind for a while. He is working at grade level, you said, so there is no big hurry to define anything at this point.
Since he does have an interest in science, I would focus on that outside of school and then try to incorporate reading and writing and math into your science explorations. If you're doing an experiment, have him read the instructions (with your help), make a checklist of supplies as he gathers them, and add or subtract amounts. If you're about to go on a nature hike, have him read about the season or the place you're going or specific plants and animals, have him take or draw pictures and label them, have him add up all the animals he sees. You get the point . . . . Make reading, writing, and math worth his time and effort. But, if he fights you, feel free to let it go and just enjoy the fun for now.
