In an effort to understand the problems and difficulties students faced in learning fractions, a study was carried out on Form 1 students from four different types of secondary schools in Perlis, Malaysia. Five different questions on proper fractions were constructed involving two fractions with equal and different denominators, and more than two fractions with different denominators. A Rasch analysis was done on the responses to help assess their level of conceptual understanding.The whole number concept was very dominant as some of the students treated the numerators and denominators separately, showing their confusion and unstable thinking in fractions learning. Keywords: Fraction understanding, proper fraction, whole number, Rasch analysis © 2017 The Authors. Published for AMER ABRA by e-International Publishing House, Ltd., UK. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer–review under responsibility of AMER (Association of Malaysian Environment-Behaviour Researchers), ABRA (Association of Behavioural Researchers on Asians) and cE-Bs (Centre for Environment-Behaviour Studies), Faculty of Architecture, Planning & Surveying, Universiti Teknologi MARA, Malaysia.