Seasons come with a problem that belongs to Thai children alone. The book teaches four seasons, not one of which they have ever lived through. No leaves turning colour, no snow. Teach straight from the textbook and all you get is recited words with no experience underneath them, and words like that are forgotten fast. The better route is to teach both systems and make the difference between them the main event.
Run two tracks side by side
Track one, the world's seasons: spring, summer, autumn (or fall in American English, which you can explain as one season with two names, like a nickname and a real name) and winter. Tie each to its standard picture: flowers opening, blazing sun, falling leaves, snow. Children have seen all of these in cartoons often enough to know them already.
Track two, our seasons: hot season, rainy season, cool season. Children have lived every one of these from the inside. Have them match each Thai season to its months and its events. Songkran sits in the hot season along with the long school holiday, and Loi Krathong falls at the end of the rainy season. The vocabulary connects to real life on the spot.
A comparison activity: here and there
Split a sheet of paper into two halves, Thailand on one side and Japan on the other, or any country your class is curious about. Ask children to draw December in both places: sunshine on the Thai side, snow on the Japanese side. Underneath they write It is cool in Thailand. It is cold and snowy in Japan. They pick up the vocabulary and, along with it, the sense that the world is bigger than the classroom window. Handing children that is part of a language teacher's job anyway.