exact value need to identify from the Vlookup

Dear All,

I am trying to compare & pick up the values across two worksheet by Vlookup.

The unique value, which compares appear in more than one time...

For example...

Student's name.....There may be cases, where John may appear more than once.
when picking up the data under John, the resultant value is not matching to the original data ?
How to resolve ?

Thanks
Mani