The purpose of the present research is investigating the effects of mathematical modelling activities on the difficulty perception of numbers sense, which is perceived as difficult by primary school 4th grade students, and achievement. The problem statement of the present research was formed as “Does mathematical modelling strategy has any effects on 4th grade students’ levels of difficulty perceptions and their achievement related number sense learning field?” The present research was conducted in accordance with quantitative research methods in two steps. The first step was conducted in accordance with survey model on 207 students, who studied in Selcuklu district of the province of Konya in the spring semester of 2013-2014 School Year. The second step was also conducted on 61 students from two equal classes of Esrefoglu Primary School in accordance with experiment model with pre-test-post-test and control group. In order to collect data for the present research, “Numbers Learning Domain Achievement and Difficulty Perception Scale (NLDADPS) Form A and Form B” were employed as pre-test and post-test on experiment and control groups, “Observation Form for the Evaluation of the Experimental Procedure” was employed to evaluate the implementation on the experiment group, and “Observation Form for the Evaluation of the Problem Solving Activities Conducted in Control Group” was employed to evaluate the teaching conducted on control group. All of the scales were developed by the researcher. It was found that mathematical modelling activities were more effective on procedural knowledge and concept-procedure connections dimensions of the topics than traditional problem solving activities, and enabled developing positive attitudes towards mathematics and contributed to the development of metacognitive skills required for establishing concept-procedure connections.