one of 和 the only one of 从句的谓语动词单复数有什么不同?

在定语从句中one of 后的先行词若是可数名词的复数,谓语动词就用复数形式,the only one of 后的谓语动词用的是单数形式.
e.g.Tom is one of the boy students in our class who are often late.
Tom is the only one of the boy students in our class who is often late.