The main purpose of this study is to assess the level of proficiency of future primary school teachers in adding whole numbers, a fundamental skill in the school curriculum. To this end, an assessment tool was designed, divided into two complementary sections: the first consisting of seven operational exercises focused on the direct execution of sums with whole numbers; and the second consisting of eight contextualized problems designed to assess the ability to apply this knowledge in real or simulated
situations. The results showed better performance in the direct exercises, where accuracy rates of 69,9% were achieved. In contrast, the contextualized problems presented higher levels of difficulty, particularly
those related to phenomena such as temperature variations, depths, and historical events that require a more complex interpretation of the statements. In terms of errors, the first section was dominated by difficulties with the use of symbols and solving combined operations, while the second section revealed errors related to reading comprehension and the formulation of appropriate mathematical models. These findings highlight a significant disconnect between the procedural knowledge acquired and its transfer to applied contexts. It is concluded that it is imperative to strengthen initial teacher training strategies, prioritizing not only operational skills, but also deep conceptual understanding and the development of competencies for contextualized problem solving. This will enable the training of teachers with a more solid mathematical foundation, capable of responding to the demands of the classroom in an effective and contextualized manner.
