The article deals with the experiences which learners have with the concept of average. This term is very common in their daily and school lives. The instruction of mathematics includes the arithmetic, geometric and harmonic mean as well as median and modus after data handling was introduced into the syllabus. Based on the sample of two different age groups of learners we were trying to find out what the understanding of the concept of arithmetic mean is, if students are more able to understand arithmetic mean as an algorithm or they can use it to solve an open ended task, and if there is a perceivable qualitative difference in the comprehension related to the learners' age. In accordance with the results we propose some guidelines in order to better understanding the concept of arithmetic and other means.