is public static DataTable GetStudents(int searchType, string searchString) a bad idea?

I've taken this course http://imar.spaanjaars.com/QuickDocId.aspx?quickdoc=419 to get al little more understanding of building a three layerded website.

(this person states that it is his way and that there are many ways to Rome but this is a way that works fine for him..)

So, i've used his code for writing methods and he uses static methods.

I've made my own. not using Lists but DataTables. Like this:

public static DataTable GetStudents(int searchType, string searchString)

 

But now my colleague says that his this is a bad idea. But to be su ...