Aims: Through this qualitative approach we intent to investigate the existence of patterns in errors that children with Down's syndrome make while counting. Study Design: The current study can be described as descriptive correlational, while we are also trying to extract data through qualitative analysis. Place and Duration of Study: In the research, took part 15 Special Primary Schools in Attica-Greece. The study conducted between September 2013 and December 2013. Methodology: The sample of the study included 40 students with Down's syndrome of moderate intellectual disability. All of them, attended in Special Primary Schools. Their mean chronological age was M = 10.07 (y;m). To include a child in the research, it was expedient that its mental age should range between 4;00 (y;m) and 7;01. As a research tool, it was used the Greek standardized version of Utrecht Early Numeracy Test. This psychometric criterion is called Utrecht Early Competence Test. Results: The widespread failure of students with Down syndrome in activities related to enumeration, led us to speculate on the existence of typology in the errors of these students. Through this research, the hypothesis of the existence of patterns was confirmed and as a result the errors classified in 4 categories. The patterns of errors included recycling parts, skipping objects, double counting objects and a mixed pattern of skipping objects and double counting objects, which is coherent with previous research in the field. We also found that the variables of Correct answers in One to one subtopic are strongly correlated with Number String Production subtopic and Cardinality subtopic having rho=0.669 and rho=0.534 respectively. We should also mention that the Number String Production subtopic and Cardinality subtopic are correlated with coefficient 0.772. Finally, it is also clear, that gender does not affect the patterns of errors since it was not found to be statistically significant. Conclusion: We focus on students' errors in order to understand not only their way of thinking, but also the way they discover new knowledge. The results are discussed in terms of their significance in curriculum design and designing of teaching scenarios.