Can someone explain how の is being used in the following sentence? It seems to be used as a conjunction to me, but I've never seen it used this way.
そう、今では公立でも５年生あたりから英会話を教えるのが当たり前なんだよね。ちなみにうちのクラスの児童は全部で３２人。内訳は男子１６人の女子１６人。
（from 小西マサテルによる「名探偵のままでいて」）
I assume the bold sentence means "the class was composed of 16 boys and 16 girls", but I expected the writer to use に instead of の.
