他曾经是一名学生 用现在完成时说。

现在完成时有个主动与被动的问题：
主动：s+have/has done
被动：s+have/has been done
他曾经是一名学生，很明显是被动的用法，故译作：He has been a student.

He was once a student.

He was a student.

He has been a student

He has ever been a student.