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.
Kawashita has a brother who is a first year student in elementary school.
This April, I’m starting the first year of middle school, my little sister is starting the first year of elementary school, my older brother is starting the first year of high school, and my mother and father are starting the first year of university.
I haven’t even learned the kanji that first grade elementary school students know yet.