This study aims to examine the strategies students at different education levels (7th-12th grade) use to examine to solve proportional and non-proportional problems. The study uses a cross-sectional research design. The study group consists of 49 middle school students, 24 of whom are in 7th and 25 of whom are in 8th grade, and 130 high school students, 38 of whom are 9th, 33 of whom are 10th, 32 of whom are 11th, and 27 of whom are 12th grade. The study uses a measuring tool created in line with the literature and it contains two problems for each of the four different problem groups, which are missing value, numerical comparison, qualitative reasoning, and non-proportional problems for the data collection. The findings of the study indicate that there were no notable differences between grade levels in the strategies used in missing value and numerical comparison problems, and in qualitative reasoning problems, high school students resorted to more appropriate strategies than middle school students. The study found that 7th, 8th, and 9th-grade students for non-proportional problems that contain a constant relationship and the majority of students from all grade levels for problems that contained an additive relationship made wrong interpretations through multiplicative thinking.

proportional reasoning, proportional problem, non-proportional problem, cross-sectional study