Before Japan had Western-style "textbooks," it had ōraimono 往来物, compilations of letter-writing samples. Ōrai 往来 literally means "coming and going," here in the sense of correspondence back and forth between two parties — although eventually the meaning of ōrai was diluted to just "textbook". Here are a bunch of such books online.

From the 14th to the 19th century, the king of ōraimono was Teikin ōrai 庭訓往来. The title literally meant "Correspondence [samples] for education at home," but it was eventually used in temple schools (terakoya) as well. It contained 25 letters dated from the first month through the twelfth, artfully crafted to cover as much as possible of the topic and vocabulary pool from which your standard social letter might draw.

Of course, it wasn't the exact same book for all those centuries. As Katsumata Masano explains:

The "Teikin Orai" had made the following development. (1) At first it was a calligraphy text. (2) By writing phonetic symbols (kana) alongside Chinese characters to indicate the pronunciation, it was used as a reader. (3) By annotation its text was linked to other texts. It became a kind of commentary book. (4) The notes were illustrated. It became a book with a lot of illustrations.

Here is a good example of the final stage of Teikin ōrai development, from 1811. (This page layout, with the main text in large print in the middle and notes/pictures in the top and/or bottom margin, is still used in many scholarly editions of the classics, although of course none of the text is handwritten for calligraphy practice these days.)

I've transcribed the first page (after the introduction), and a bit of the second, below. Kanji are left as written, but kana have been punctuated and rearranged into reading order — note the kaeriten to the left of the relevant kanji. The English translation is mine, but I have elected to use surfer English to remind readers that upper-class medieval correspondence about courtly goings-on is not my strongest suit. Also, I was at the beach this morning.

春始御悦向貴方先祝申候訖
富貴萬福猶以幸甚々々抑歳
始朝拝者以朔日元三之次可急申
之處被駆催人々子日遊之間乍思
延引似谷鶯忘檐花苑小蝶遊
日影頗本意背候畢 [...]

はるのはじめのおんよろこび、きほうにむかつてまづいはゐまうしさふらいをはん。
ふつきばんふく、なをもつてかうぢん／＼。そも／＼、としの
はじめのてうはいは、ついたちぐあんさんのついでをもつていそぎまうすべし
のところに、ひと／゛＼ねのひのあそびをかりもよほさるるのあいだ、おもひながら
えんいんす。たにのうゞひす、のきのはなをわすれ、そののこちょうのひかげにあそぶににたり。
すこぶるほんいをそむきさふらいおはん [...]

Early spring is such a buzz and I totally sent good vibes your way, dude. Wealth, health, happiness, and all that good stuff. Anyway, you know that normally I would totally go and pay my respects to the court (朝拝, chōhai) on new year's day. This year, though everyone was so wrapped up in the day-of-the-rat games (子日遊, ne no hi no asobi) that I totally missed that wave. Man, I feel like a nightingale in the valley that forgot the flowers on the eaves, or a butterfly in the garden hot-dogging in the shade instead of the sunlight ー it's totally not the real me, dude. [...]

And two terms are glossed above:

朝拝　てうはい
元日たつのときに天子大こく殿にておこなはせ給ふこと也
Chōhai: Held by the Emperor in the hour of the dragon [about 8 a.m.] on the first day of the new year, in the Daigokuden

子日遊　ねのひのあそび
正月上のねの日に人々野べにいでて小松を引奉なり
Ne no hi no asobi: On the first day of the rat in the new year, people go out into the fields and pick young pines