This study aims to describe students' mathematical reasoning ability in
completing non-routine questions. Subjects of the study were class VIII B
of SMP Gunungjati Kembaran. Sample of the study was selected by
using purposive sampling technique. Students were grouped based on
the achievement; high, moderate, and low. Data of the study were
collected by using test and interview. Results of the study concluded
that: (1) students having high achievement have performed
mathematical reasoning ability, because they are able to draw
conclusions inductively and deductively with coherent and logical
explanation; (2) students having moderate achievement are not able to
fully performed inductive and deductive mathematical reasoning ability,
because in the process of drawing conclusions, it has not fully show
coherent and logical steps yet; (3) students having low achievement
have not demonstrated mathematical reasoning skill yet, both inductively
and deductively since they are unable to draw a coherent and logical
conclusions.