Background: Research has shown that mathematics anxi-ety  negatively  correlates  with  primary  school  mathematics  performance,  including  fraction  knowledge.  However,  re-cently no significant correlation was found between fraction arithmetic  performance  and  state  anxiety  measured  after  the  fraction  task.  One  possible  explanation  is  the  natural  number  bias  (NNB),  a  tendency  to  apply  natural  number  reasoning in fraction tasks, even when this is inappropriate. Students with the NNB may not realize they are answering incorrectly.

Aims: The  aim  is  to  examine  whether  a  misconception,  namely  the  NNB,  can  influence  students'  fraction  state  anxiety.

Sample: The  participants  were  119  fifth-  and  sixth-grade  students categorized as belonging to an NNB group (n = 60) or  a  No-NNB  group  (n =  59),  according  to  their  NNB-  related answering profile on a fraction arithmetic task.

Methods: Group differences were examined for state anxi-ety and performance on a fraction and a whole number arithmetic task and self-reported trait mathematics anxiety.Results: The NNB group reported lower fraction state anxiety than the No-NNB group, but there was no signifi-cant difference in trait mathematics anxiety. Furthermore, the NNB group reported lower fraction state anxiety than whole number state anxiety, while the opposite was true for the No-NNB group.

Conclusion: The present study suggests that students' per-ceptions of their own performance influence their state anx-iety responses, and students with a NNB may not be aware of their misconception and poor performance. Not taking into account qualitative differences in low performance, such as misconceptions, may lead to misinterpretations in state anxiety-performance relations.