This paper explores misconceptions about locating integers and decimals on horizontal and vertical number lines as revealed by the students‟ responses enrolled at Federal Government Secondary Schools in Islamabad. The instrument was a test based on 4 parts containing integers and decimals placing on horizontal and vertical number lines. 368 students were the sample of the study. The analysis of students‟ incorrect responses ranged from 4% to 62%. The analyses of students‟ incorrect responses helped for the investigation of students‟ misconceptions. Four misconceptions leading to incorrect placement of integers and decimals were identified. The opposite sign misconception appeared when students placed positive integers in negative region and negative integers in positive region of number line. The other two misconceptions Translating Positive Interval (TPI) and Translating Negative Interval (TNI) appeared by creating the positive and negative part of the number line which emerged through the negative and positive intervals. The „decimal-point-ignored‟ misconception was identified when students ignored decimal point and considered the remaining part as whole numbers on horizontal and vertical number lines. The implication for the students and teachers is that, teaching of integers and decimals should not be confined to conceptual understanding only but also through the visual description on number lines which must be focused during teaching.
Keywords: Misconceptions, negative integers, positive integers, decimals, horizontal number line, vertical number line.