I think the last classroom I worked in, prior to leaving to be SAHM after the birth of my daughter, was a great example of what a preschool program *should* be.
It's in an elementary school, run by the district--so the head teachers are people with 4 year degrees in early childhood and in our case, though maybe not *all* in the district, special ed.
The assistants (my job) were either people who'd completed 2 years of college at least, or passed a district exam, besides having experience working with children. And well-enough paid, with benefits, to keep turnover *fairly* low--pretty unheard-of to have the full-time (well, to the children, it was 4 days a week, kid hours) person change in the middle of a year, and very common to have the same person there for years. (a not at all common thing in other places I'd worked)
The classrooms were mixed-age 3-to 5-6. And mixed in about every other demographic--disabilities, income, you could qualify by Head Start or another income-guideline, slightly higher--if it was your neighborhood school, or by IEP need. (developmental delay or disability.)
The largest class I had was 16 at the end of the year, and we got an extra aide when that morning group hit 15. (We took kids who qualified by IEP anytime, up to a max of 17, though we never hit that.) So the ratio really *never* exceeded 7 children per adult, typical was more 5-6:1 or less. (In our state, daycare ratio for age 3-5 is 10:1)
Our typical day included an outdoor recess of 20 mins, in the gym if it was bad weather.
A "circle time"--sit at the circle, read a book, possibly talk about something, do a nursery rhyme and a calendar activity, who is present/absent, a welcome song, welcome new kids, all that kind of thing. (Preparation for kindergarten--sit and listen and participate.)
A choice reading-or-written language time of about 10 mins.--read a book with an adult or alone, or use the writing table or write on the whiteboard. (We started the 'written language' when we noticed children were not choosing to do this at work time--gave us a chance to focus on it and encourage it.) It was *not* academic per-se, kids could draw, or whatever, but children would often *want* to work on writing their name or other things.
A snack, of course--with adults trying and encouraging (but *not* FORCING) kids to try foods, or to even eat.
A small-group table time. OP, you mentioned your son being "advanced" reminds me specifically of one little boy we had who was barely 4. Our tables were loosely grouped by "going to kindergarten next year" and those who were not---but we *definently* had development in mind as well---this little boy I'm thinking of went to the "kindergarten" table a year early because that is where he needed to be--he knew all his letters, he could count as high as we could listen, he was writing his name, etc.
We also had some fairly open-ended activities that could accomodate any ability level with not much change.
That was the time of day where we really focused on kindergarten-prep activities for the older kids, some more academic than others. (there were some simply fun ones too, like a few cooking activities, the time we painted pumpkins

)
Then there was an hour or a bit more (out of 3-31/2) spent in child-chosen center play and the clean-up and talk about what they chose (the house, another 'dramatic play' thing like fire station--or one year, TV repair, yes with real tools on an actual-non-working set,

we had lots of 5 year old boys that year...) art corner, sand/water, the oft-ignored writing center, book corner, blocks, train set things like that, you get the idea.
(that was another really neat thing, we always had the "house" set up, and then another "scenario" prompted by the kids' interest, in the idea that most play involves somehow, a home, because that is what kids are most familiar with. The person who goes to the doctor gets sick at home, the fire fighter leaves the house to go to the fire, etc.)
Oh and we had a "large group" activity at the end--usually involving music and often large-motor.
So...to sum up....the kids were in school about 3 1/2 hours. A good 90 minutes at least of that time was spent in play totally chosen by them. (the centers and outside/gym--well, in the gym, we picked the equipment for the day, but it was pretty much free within that.) The rest of the time was mostly teacher-guided/directed, but with lots of room for child input. (large group might be dancing to a song the kids requested, they get to choose their books and whether to read or write, and what writing materials to use, even within the small group activities, there was usually a lot of room for child creativity and varying-abilities with open-ended materials. Very few of those activities were "sit down and do XYZ this way."
(one example I'm remembering from small group was these little letter beads and string---our youngest kids might be simply learning the coordination required to string beads, then some might be doing things with the colors, others might know a few letters and talk about them, and still others might make a 'necklace' of their name...with certain colors for the letters if they got that detailed! Totally child-led though, if they weren't at all interested in trying to spell their name, for example, nobody forced it. There was value in the fine-motor aspect, participation, interaction, talking about colors and letters, all of it, not just in an end product. It wasn't about *one day* and *one project* there would be another time when they *would* be interested in a more 'academic' thing. But still teacher-directed, and kindergarten-prep in the sense that during that time, they could not run off and do something else entirely.)
So I'm saying *very little* "do a worksheet" type work. (I can think of ONE thing we did in 3 years that was cut out these pictures and put them in the right order for a story)
Lots of child-choice, even within teacher-directed activity. (you need some teacher-directed activity if you're preparing to go to kindergarten in a typical school setting.)
Yes to academics, but as it's driven by the child's interest! Yes, learning about letters and numbers should be encouraged, but not FORCED...their interest will come if they see it going on around them!
Multi-age grouping. I love this so much I've special-enrolled DS1 in a school with multiple opportunities a day for *all grade* interaction K-5. There is just a lot for them to learn socially and their interests grow from what they see the "big kids" doing. In a good way.
but it needs to be where nobody is pressured--there's no *pressure* on anyone who just isn't yet interested in things like learning to write their name. IT WILL COME. I have seen it enough times now to have faith that it will, within a generally supportive environment that provides the opportunity for it.
And there's a lot to be said for inclusion---I *loved* watching the "helpers" develop in the class.

AND the child with the SN growing and thriving on interaction with 'typical' peers. This is an age where kids are very accepting and I *hope* though I haven't followed it, that it helps them to grow into people who are generally accepting, tolerant, and willing to give someone "different' a chance. (and yes, I've seen this work with some pretty involved needs--a non-verbal child in a wheelchair who participated fully and loved to paint, do sand and water play, block corner with vehicles sometimes--everything anybody else did that suited his interest.

He even had a mom--with a child with autism who had previously not shown any particular "friend" interests--asking to arrange a playdate with him because her kid talked about him and wanted it! )
But....I will add this caution---the particular head teacher in my room came from a background of working with children in a special school--so TONS of experience with severe special needs. It might not be as great as it was without someone of her background and desire to accomodate and include.

(and I'll admit I'm of the same mindset.)
sorry about the novel as you can see I loved my last job and I really thought we had something great going.
