"You are a good teacher, Samia."
Translation:أَنْتِ مُعَلِّمة جَيِّدة يا سامْية.
Both of them are used in everyday speak....but You may hear أستاذ more often because it is more common than the two before especially in schools...
The word معلم is used in places like resturans/small job placs etc... i mean jobs that you learn by practicing it not by academic achievements, so here the manager/teacher/coach are called معلم ... İn a restaurant if the waiter want to say "the manager wants sth...." You say in Arabic: "المعلم بدو" ... This is not used in MSA though