I have been studying Korean for a long time, but I do not remember ever reading or hearing the word 솎다. I may have read it and just forgotten it, or I may have heard it and not realized it, but, at any rate, I stopped and looked up the word last night while reading the story. 솎다 means "thin [cull] (out) plants." I think that is a useful word, but I have to be careful when pronouncing words with a "소" in them because if I am lazy about rounding my lips, they come out as "서." In fact, I have learned to take special care when pronoucing any word that has an ㅗ sound in it since Koreans seem to be very particular about their ㅓ's and ㅗ's.
The story refers to students in the fourth grade as 상급생, which means "upper-class students." It implies that fourth, fifth, and sixth grade students are considered "upper-class students," and first, second, and third grade students are "lower-class students" (하급생). I do not remember hearing such designations when I was in elementary school, even though we may have felt that way.
Finally, the story begins with the following sentence:
경호네 班에서는 4學年이 되어서 처음으로 學級 어린이會가 열렸습니다.
After becoming fourth-year students, Kyeong-ho's class had a grade-level student meeting for the first time.
What caught my eye in the above sentence was the use of 네 after 경호, where it is used instead of 의 to make 경호 a possessive noun. I have known 네 to be used in this way to refer to one's family, but until I saw it used in the above story, I never realized that it is also used to refer to other groups. I may have heard it used, but just assumed that it was 의 since 의 and 네 sound similar in spoken Korean. Now that I think about it, I have seen it before, but just never paid attention to it. In fact, I saw it in a cartoon that I talked about here.
I have noticed that when I read fairly easy stories, I pay attention to smaller things, things that I tend to overlook in more difficult stories. I think that is a good thing.