The importance of critical thinking in education is underpinned by decades of theoretical
and practical work. Differences have been demonstrated between students who receive
education in this area from an early age and those who do not. However, not enough work
has been done to measure these skills in a classroom setting. Given that the best time to
teach critical thinking is during the first years of primary education, we designed a test
to determine the level of critical thinking among 3rd and 4th grade students in Language
Arts using a graphic novel. We showed the legitimacy of the instrument through Construct
Validity, Content Validity, Pearson product-moment correlation, Reliability and Item Analysis. Using the instrument, we studied how critical thinking skills differ among 3rd grade
students, according to their socioeconomic status (SES), studying schools with low, middle
and high SES. We found significant differences between the schools, which suggest that
there may be a relationship between socioeconomic status and the development of critical
thinking skills. The test presented in this study is an improvement on existing assessment
tools as it replaces unidimensional models with models that provide a more detailed and
multidimensional picture of student learning.