Every one of?

readok2009

Every one of the students had to do their own experiment.
Every one of the students should have their own books.
（正式用法是用单数his，但实际上的使用是their多于his。）
但我想请问的是，在用了their的前提下，后面的名词（experiment、books）
是该用单数还是复数呢?