Lucky you! 
As a late-blooming, academically inclined, bigger-boned, frizzy-haired middle schooler, it was possibly the most mortifying experience of my life. All those people, looking me up and down, smirking, and saying, “So…you want to be a model?” ::dies of self-awareness & embarrassment::
Curly hair, few inches below the shoulder. I wash 1-2 times a week, blow-dry/straighten. Don’t do anything else the other days other than brushing it. If I am headed out for a wedding or a party, I might straighten it just before. No products. Both D and I have found that our hair looks really good and styles really well the day after we wash it.
I have long, thick, coarse, wavy hair and I wash twice a week, generally. I prefer air drying, but my hair takes forever to dry on its own. I work from home Monday and Friday and go to the office Tuesday - Thursday, so I wash and air dry Monday night, then style with hot brush or use old school hot rollers for long hair on Tuesday morning. I can then get away with not washing again on the days I drive to work, which saves me a ton of time since I already wake up at 4:30 and have an hour commute. I’ll wash again Friday morning or evening, depending on when I might have Zoom meetings during the day. On Sundays, I just hope that the dry shampoo saves me so it looks presentable enough for church 
I’ve found using a good clarifying shampoo once per week helps with hard water and dry shampoo build up. I don’t use many products other than heat protectant, but I do use a mask each week on the day I use the clarifier.
When it needs it. Thick curly hair here. Depends on what I’ve been up to. Summer frequently (at least a good rinse after swimming, exercise). And less during winter.
Can you give an example of a clarifying shampoo?
@abasket Neutrogena makes a clarifying shampoo. It works great for getting product buildup out of hair. I’d be careful though using any clarifying shampoo on color treated hair. It might wash out the color.
It was “Charm School” when I was a tween, and the courses were held on three or four (?) consecutive Saturday mornings at our local Sears. We walked with books on our heads, sat up straight, crossed our legs at the ankles, and learned about feminine hygiene, hair care and styling, light makeup application, and how to dress modestly but attractively. It was all about “poise,” being “ladylike,” and looking our best so that we felt our best and, thus, confident. And, of course, all the clothing and products were available for our convenience right there at Sears. I actually enjoyed those classes.
The one I use is Ouai Detox Shampoo, and I use their mask for thick hair as well. They are not inexpensive, but because they only used once per week, it softens the blow to the wallet.
@mom60 makes a good point about chemically treated hair. I do not have color or highlights, so I don’t worry about that.
I also went to Charm School, but for the life of me I can not remember if it was at Sears or Macys (then Davidsons.) I believe my mother thought it would help her tomboy daughter; it didn’t, but boobs, high school and boys did!
My hair is straight, but will frizz if not blown dry and flat ironed. I need to wash it twice a week, but if no plans for the weekend, wait and wash it on Sunday nights for the work week; the weekend is spent in a hat.
I clearly lived in a different universe. Charm school I thought was in the 1800’s. It was in the US? I knew I was culturally deprived growing up. But, this surprises me.
We called it cotillion if it was co-ed. My sister got to do it, but I did not. (We moved to California for my middle school years before moving again.) I did have an aunt who made sure I knew how to stand and sit gracefully.
My S23 did cotillion back in 7th grade when we happened to be living in a city for those two years. Dancing, shaking hands, small talk. So that is 21st century.
I still try to impress my family by walking, turning, and then jumping up and down with a hardback book still flat on my head and not falling. Good posture is important.
They are not impressed. 
I didn’t wash my hair yesterday, and by this morning it was looking icky. I thought of this thread as I washed my hair this morning. 
It’s STILL a thing, but more like cotillion (where you also learned to dance). I had friends that sent their kids to our local version (I am blanking on the name, it was something more generic), where they learned which fork is the salad fork and how to dress up and go to the dance and how to be a genteel guest or host.
My brother and sister went to cotillion, but I declined my mother’s invitation and I was the youngest so I think she was tired of pushing the point by then.
My husband went to cotillion, too, but after a few sessions he started skipping it to go play basketball.
I have no idea if cotillion or whatever they call it now addresses hair washing frequency. I will say some people just have oilier scalps than others. My husband needs to wash his hair pretty much every day or it will get greasy. I could probably go a week before mine would get noticeably greasy to others, but it would feel dirty to me if I went a week. I can easily go 2 or 3 days, though, and could probably stretch it to 4. I do think it looks better freshly washed, but it looks good if I skip a day, too. I think it would start to get pretty flat if I skipped 4 days and I like it to have some curl so I wash it usually every other day or maybe skip 2 days.
Based on @Sweetgum’s description, USMA has cotillion. The academy is still teaching cadets how to be dashing, proper, and genteel in Society. “West Point–Finishing cadets at taxpayer expense since 1802.”
Our son has no hair to wash, though.
These charm school classes were offered by the two major department store chains where I grew up, and they were very well attended! I went…it was actually fun.
And yes, good grooming including hair care was discussed.
I think that is the key- growing up we had no major department stores, nor did our kids where we raised them. They did however have an REI…and mountain lions. 
It was not offered by department stores when I was growing up, nor when my kids’ friends went to “Social”. (I asked my friend and it was called Ourtownname Social. )
And it is still a thing. I looked it up since she gave me the right name. It says children learn “social skills and responsibilities, and social dancing”. And " Specifically, the program teaches children ballroom and contemporary dancing, as well as guidelines and responsibilities for social situations they will encounter throughout their lives. These responsibilities emphasize courtesy, kindness, and respect for others. The particular goal of Social is to make courtesy and respect habitual in ordinary situations children experience every day." Also, “Boys wear sport coats or suits, ties, dress shirts and slacks, and non-athletic shoes. Girls wear dresses or dressy skirts and blouses or sweaters and non-athletic shoes.” It has another bit about “appropriate host and guest behaviors”.
Totally not my kids’ thing, but I think they learned a lot of that by osmosis from us. Although not how to do the Foxtrot. We didn’t teach them that.
Here’s an article: What You Really Learn at Cotillion Class
And definitely still a thing. There’s a “National League of Junior Cotillions” https://nljc.com
As I age, I have a lot of thin hair. My haircut is just below my shoulders and layered. I wash it every 3/4 days. It is always up in a pony tail or a twist that last day before washing. I use a volumizing mousse and the Revlon brush blowdryer for smooth volume. I do rinse off in the shower but my hair is pulled up and does not get wet in between washings.
This seems to much more healthy for my ends and my color.
In the summer I swim and have to wash more often. I do use a spray on protector for the sun.
No such a chapter in New England. No wonder why I have never heard of it.
I wonder why not in New England?
I also use old school hot rollers every day (ha, have done so since a teen). Since I wash my hair 1-2x a week, just pop in the rollers for a few minutes in the a.m. and hair looks finished (even sorta like a blow-out). For me the trick is very large rollers (2" b/c my hair is long and I like the straight, rather than curled, look). I keep the rollers in for about a min or two while brushing teeth, etc. Saves soooo much time in the morning and hair washing is not for styling, just cleanliness LOL.