>>6
I wouldn't be too quick to criticize another's Japanese. If you want to get technical, 小学生の時に is incorrect. Because it's such a large span of time, you do not use に. Rather, it should just be 小学生の時、yada yada yada.
You only use に with 時 when speaking of more narrow spans of time. It's not an exact science, but you can bet that six years of elementary school (or 5) is much too broad to use に.