Match values from different data frames and add a column to one data frame with data from the other data frame

Question

I am trying to match data frames and then add data to one of the data frames using a column from the other data frame. For example:

name age weight           name grade 
John  17   145            John  87
Amy   18   130            Amy   89
Paul  17   160            Paul  92

I want to match the names and add the grades to the first data frame:

name age weight grade          
John  17   145   87          
Amy   18   130   89        
Paul  17   160   92