PROC SQL joins SCORE and STNDTEST to create a table (COMBINED) that contains standardized and original test scores for each student. Using AS to rename the standardized variables NEW.TEST1 to StdTest1 and NEW.TEST2 to StdTest2 makes the variable names unique.
proc sql;
   create table combined as
   select old.student, old.studentnumber,
          old.test1, new.test1 as StdTest1,
          old.test2, new.test2 as StdTest2,

   from score as old, stndtest as new
   where old.student=new.student;