For context and perspective, I am an autistic, I have a leadership position at the children's hospital I have worked at for over 35 years, and am an adjunct instructor at a local university.
With the so-called "high-functioning" autism variants (Asperger's/ASD-1), especially those with higher IQs, motivation can be difficult. Many of us will spend a fair amount of time trying to sort out what we think of as "needed" versus what may be required in order for progression through an academic program. Obviously, there may be steps along the way that appear to be in conflict, from the perspective of the autistic. Many of us do not do well in groups. Many of us will try to find "efficient" ways of doing things, and again, it may not be a way that is acceptable to the instructor. To the instructor, this may appear to be a form of "intellectual laziness", but a second look may reveal a more keen insight into a "first principles" way of thinking that is often not appreciated, nor supported.
Many autistics may be described as visual learners and tactile "hands on" learners. Sitting in a classroom listening to lectures, doing math problems, writing papers, etc. is NOT how a typical autistic person learns. We learn by doing and experiencing. For example, in physics lab I could tell what was going to happen, how an object would move, how far it may travel, the types of forces it could handle before failing, with a high degree of accuracy, etc., but I struggled with the mathematical proofs. I had a near perfect score on the science portion of the ACTs and SATs, even though I took the tests the summer before the 11th grade in high school and had never had a science class since middle school. Why? I was an observer, a tinkerer, I pulled mechanical things apart and reassembled them, I grew plants, I studied the stars, I had good pattern recognition, so on and so forth. I had a good understanding of how the world works without the formal education. In my life, I have modified and raced my own cars and trucks, learning how to weld, to engine build, and program the computers. I have completely gutted a home and rebuilt it for resale, doing all the electrical and plumbing work, which required taking the electrician's licensing test at the township office. I have built computers. I have created a 300 gallon natural ecosystem aquarium (no filters, completely balanced). I am currently designing a high-tech, off-grid home with geothermal, solar, wind, passive solar, and battery storage, with an attached greenhouse for my wife and I.
Keep in mind, I did not like school. The thought of school only brings back bad memories. However, my point with all of this is that the combination of all the sensory issues, communication difficulties, social difficulties, and neurodivergent-type of thinking does not fit well with the curriculum and environment of most schools. Intelligence has nothing to do with it. It's the environment and the lack of intellectual stimulation from the perspective of the autistic individual. School can be quite boring and mind-numbing to an intelligent autistic, and grades will suffer because, frankly, many of us, right or wrong, don't see much point in it, especially when we are young and ignorant of the world. If you can tap into his "special interests" if he has any, and can make some connections there, it can be helpful.
I think trying to understand his perspectives on things will be helpful, but trying to force a curriculum into his brain WILL fail.