Child That Doesn't Deal Well with Unpredictable/not-on-the-list Stuff...

For a kid who doesn't like surprises, you should try and make surprises fun. Tell him you're going to go grocery shopping but drive to the ice cream parlor instead. Surprise! We're having an icecream instead!

See how he handles it. Switch things up until he gets used to it, and even anticipates surprises, because you've shown him that they can be fun. That way he may be able to better handing the rapidly changing environment of a classroom.

/EDIT - Had another idea. Instead of making checklists of things to do, try writing down a bunch of assignments that need to get done on little slips of paper. Fold them up and put them in a clear ziplock bag. Don't let him see what you've written down. Have him pull out a paper at random and that's what you do first. This way, he knows there's a bunch of things that need to get done, because he can see there are many folded papers in ziplock bag, however, he won't know what they are until he's done with one task and must pull out another. That would be another way to get him used to completing a series of tasks without having him know what they are beforehand.

When you write a shopping list, try to make it more vague as well. Instead of writing down Broccoli and Corn... put down "Vegetables" that way you teach him leeway when it comes to the grocery store. Instead of rigidly sticking with broccoli and corn, perhaps you see that string beans are on sale that day and you want to pick those up instead. By writing "Vegetables" on the list, you remind yourself you need a veggie, but you can figure out what one when you get to the store! =)

My son does not do change well, either. He is now in college and has learned to deal with it.
If I could make a situation, predictable for him but give less information - I did. Sometimes I would just tell him we were going out. I stopped telling him which stores we were going to. I stopped telling him everything. If we were going to lunch with a friend, I'd just tell him that we were going, but not where. If he asked where, I'd tell him he'd know when we got there.
I put my son in Karate. This helped him immensely. I suggest you put your son in karate - they will teach him self control, self discipline, coping skills, and more. This will really help him.
My son is now at a military college -- it's very structured and he likes that - a lot! He is on an Army scholarship and will be commissioned upon graduation. Everything they do is structured and he likes that. They give them plans, contingency plans, and more contingency plans-- it's perfect for him.
Your son will find his place, too. :-)
LBC

My nephew is highly intelligent and on the highly functioning end of the autism spectrum, so much so that they actually do not really know what it is and call it: PDD-NOS = Pervasive Development Disorder Non Specific. He could tell time and read at age 4, he could draw with perspective at age 5, he is intellecually gifted but that often comes with emotional "giftedness" as well, and in his case he wanted predictability as well. However, you are not stating some of the social (difficulty understanding cues and making friends) or emotional (tantrums) that goes with this diagnosis. If it worries you I would speak with his pediatrician and perhaps have some testing done by a neuropsych who can determine his learning style and (dis)abilities.

http://www.nationalautismresources.com/autismsymptoms.html

Pay attention to what teenmom said below because you did say he was aggressive. There is a difference between kids who freak at unpredictability and other kids not behaving (my daughter) and those for whom the freak out turns into socially really unacceptable behavior. My daughter is highly anxious and so intensely dislikes when other children do not behave. It took a lot of cognitive behavioral work to get her to cope with it. A child with a PDD or even OCD who becomes aggressive is in another category. You and your pediatrician need to figure this one out.

He sounds like a great and very bright kid and he is lucky to have a mom who sees him for who he is and wants to develop him as himself!! Good for you and him! It's just going to be a bit of a puzzle.

Have you told the therapist in detail the things you have told us here? The therapist would benefit from hearing these exact examples (without your son present, of course -- children hate to feel "talked about."). You're correct that this does need attention now.

While it's good that he is organized, you already see the potential here for problems if he encounters anything outside his lists or even his mental "list" of what each day should bring. The therapist should be giving you ways to handle this at home and introduce uncertainty and new experiences in a gradual and positive way. It is vital for a child not to melt down when something new happens. I know a girl (now 11) who has issues with changes or unexpected shifts (school schedule changes; or she is asked to learn a new dance at Girl Scouts and suddenly decides it's impossible; or there's a school field trip and she gets overwhelmed with the constant movement and change and melts down, etc.). She has benefited from therapy and some medication.

Homeschooling him is great, but does he have any homeschooler classes with other homeschooled kids yet? Do you have him in any homeschooler groups for certain events or classes? That might help introduce him to being with other kids in an academic or "field trip" situation. You are right to be working on this now because an older child with issues about change has a very tough time, especially if there is aggression coupled with it. Be sure he's evaluated for the full range of learning and emotional issues related to both aggression and his need for absolute predictability.

I have a son that is VERY much like your son. We call him our black and white baby. There is no gray area with him. Needless to say, we did experience the total opposite with school, he LOVES the structure but has a teacher that does not vary outside of the exact same structure every day and is very list oriented. I dread the day that he has a teacher with a loose structure, I am positive he will severely struggle. Since your son is only in kindergarten, I would not worry too much, he is who he is and just needs time to learn how to incorporate his personality into mainstream. Kindergarten is huge on teaching this to kids. Maybe you might consider having him do kindergarten again at school next year. Maybe age-wise he will be a bit older to flourish and learn to deal with his structured ways. The only down side is he will be very ahead academically. Who knows, maybe 1st will be better for him since all the kids will be older and they will work better together. All I know is kids do tend to work through their personality hiccups and as parents sometimes we need to let them do that so they have a chance to figure it out.

Good luck!