The aim of this research is to propose indicators of epistemic and mediational suitability to assess tasks designed in a mobile learning context, using theoretical and methodological elements of the onto-semiotic approach (OSA) and the SAMR model (substitution, augmentation, modification, and redefinition). With these indicators, 110 tasks designed by two Mexican teachers are evaluated, for the teaching of the natural number in primary education. Some results indicate that the situation-problems addressed the meanings of numerical sequence, operational, ordinal, and measure, and that 56% of the tasks were located at the substitution level. Some implications derived from the research are that the mathematical content can be complemented by including other representations of the natural number and that the design of tasks that are positioned at the modification and redefinition levels should be encouraged. The foregoing serves as a basis for the design and assessment of mobile content for the natural number concept.