You are a middle schooler now, but you're still taking baths with your mom?
Even a junior high student knows that you should choose your battles wisely.
When I was a middle school student, the biggest lie I said to myself was, "I can remember that without writing it down."
You've seen 学生 (means student). Now let's look at a student who's in the middle. Perhaps we can call this a middle school student or a junior high school student, depending on where you're from.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.