I'm not familiar with "left inner" joins. But a anti-join will do what you want. Maybe they're the same thing.
A = load 'file A';
B = load 'file B';
C = cogroup A on studentname, B on studentname;
D = filter C by COUNT(B) == 0;
E = foreach D generate flatten(A);
This will do an anti-join. It cogroups everything in A and B on the same key, filters out any groups where there have records in B, and then flattens the grouping of A so that you again have individual records.