"The teacher on duty is Emilian"
Translation:Mwalimu wa zamu ni Emilian
slightly different connotation. The English sentence is more specific about who the teacher on duty is. If you were to begin with 'Emilian', you would phrase it as "Emilian ndiye mwalimu wa zamu". "Emilian ni mwalimu wa zamu" translates to "Emilian is a teacher on duty", which is slightly ambiguous; is he one of many? Is he just on the roster of teachers on duty?