Introduction.

Lack of motivation in science education is increasingly worrying. From the Theory of Self-Determination, many and varied investigations have tried to approach a better understanding of motivation by studying different contextual variables. Among these variables, textbooks are especially relevant elements, given their important presence in classrooms and their, in principle, competence character that supposedly makes them a motivating resource.

Objective.

Therefore, the aim has been to design and validate a scale to measure the relevance of science textbooks, from this motivational competence perspective, for students aged between 10 and 14 years.

Method.

The design took as reference the existing theoretical framework and, for the validation, a quantitative methodology was implemented, using a survey technique.

Results.

The exploratory and confirmatory factor analysis revealed the existence of a single factor, achieving adequate adjustment rates. Likewise, the instrument showed adequate internal consistency, temporal stability, composite reliability, and convergent validity. Finally, the positive and significant correlations obtained with the educational motivations and inversely with demotivation evidenced the external validity of the instrument. Conclusions. Consequently, it was concluded that the scale was valid and reliable.