Gabriel Mariech Makoi of Don Bosco Primary School occupied the first position, scoring 87.4 percent.
The Directorate of Education in Tonj County on Thursday announced the results of its mock exams, Radio Don Bosco reports.
The directorate said John Jok Dut Jok also of Don Bosco took the second position with 85.4 percent and Marko Machar Majok became the third.
It disclosed that Mary Athieng Madut was number nine among the top ten students.
324 candidates from Don Bosco, Kalkuel, Magordit, Tonj Academic and Makerdit Primary Schools sat mock exams on September 14.
166 pupils passed and 158 pupils failed in all the five primary schools in Tonj.