The person to you spoke is a student Grade Two
先来分析下,the person做宾语时候,换一种表达就是（这句话拆开）：
You spoke to the person.The person is a student in Grade Two.（后面一句补充说明the person）
合成一句就是：You spoke to the person WHO is a student in Grade Two.(这里用WHO是因为在这句中the person做从句中的主语所以用who)
但是为了要突出the person,所以把the person 放前面做主语,那么它就成了You（spoke to）的宾语,所以用whom,就成了
The person (you spoke to WHOM )is a student in Grade Two.
（这里的WHOM还可以省略哦）
这是我的分析,仅供参考.希望对你有所帮助.