Find a diagram of the board set up and leave it available. He can copy that pattern or not, but he'll realize there is a pattern.
And it's cool when the chess pieces on the chart don't look exactly like his own.
Maybe check out a book on chess pieces or history of game boards. Not on chess strategy at all, but on gaming history so he can see the history of the pieces and the different forms. Or if you're near a games shop, wander by and look at different chess sets on display. it will be like a teeny chess museum.
It doesn't have to be done at any one moment, just incorporate his interest in chess pieces into your daily considerations until the time when he knows more about it than you do (unless you're a whiz, and then sorry for the assumption that you weren't).
One way for moms who love to checklist their days to provide without managing is to go afield of verbal presentation. Go through a list of the senses. And if each day you try to provide something interesting to taste, touch, hear, see and smell, his day will be more full than flat. Too many families stop at things to hear and see. (Because school stops there, I guess.)
But you don't have to do this until he's 17. You can do it until you're confident that he's filled with experiences to cross-reference at his own leisure (in dreams, in fantasies, in future incidents which remind him of those, etc.) and you feel satisfied that you're not a slacker.
If just "the five senses" seems a lame checklist and you want four dimensional instead of three, maybe each day work into conversation something about the past and something about the future. (I can hardly imagine a day without those coming up naturally in my own family, but in case you're not really talkative or something, it's something for the checklist.) If it comes up naturally in conversation you could say "They didn't even have chainsaws until... [whenever little gasoline engines were common, or whatever the seminal technological feature is] and would have had to do all this with a hand saw, or an axe." (That's if you cut firewood with a chainsaw, not if you're sitting around working a jigsaw puzzle of tiger cubs in the forest.) Or you could say "How long do you think we will have these dishes? When too many are broken, what kind should we get next?" (if you have a girl with those sorts of interests). Various kinds of mind-casting conversations into the past (personal past or technological past or cultural past or planetary past) or into the future (tomorrow, next year, next century) help kids build their internal model of the universe. I know I've used that phrase half a dozen times talking about unschooling, but I think it's one of the coolest ideas.
At school, there is a model of knowledge they're hoping to insert into each child's head. And it has things that are dumb and arbitrary, like that the history of England is way more important than the history of China (in English speaking countries, there's a lot of justification for that, but still, let me run my imperfect little thang here), and that there are some authors EVERYBODY has to know, and others that are TOTALLY optional, marginal, don't even brag if you've read them. And that some historical cultures are hugely more important than others. And some science is FACT and some is marginal "whatever," not appearing in this book.
School kids don't know the world is a million times bigger than school's version of it.
Unschooled kids are also making a model of the universe inside them, but they're making it their own way, and they're not valuing the school-bits over the bits that their model has which are unique to them and their own personal interests and experiences.
That's the main reason I think that an unschooler's checklist should look
more like the five senses and past/future than like "science, history,
language, math, maybe-music-art-physical education." Because that model is
prescriptive and limiting. And the other is descriptive and unlimited.
