"Find the last names of all the teachers that teach GELL TAMI.
SELECT T2.lastname FROM list AS T1 JOIN teachers AS T2 ON T1.classroom   =   T2.classroom WHERE T1.firstname   =   "GELL" AND T1.lastname   =   "TAMI"
teachers that teach a specific student (GELL TAMI) refers to JOIN operation on tables where student's name matches; extracting last names of those teachers.