Considering the crucial role of education in offering mitigation and adaptation strategies for climate change, there is a clear need for objective tools to assess its impact on the understanding of the issue among secondary school students. This paper describes the methodological design used to build and validate an instrument that explores secondary education students' climate change knowledge. The design is organized into several steps: literature and document review; item design; Expert judgment; pilot testing; and instrument quality criteria analysis. Thus, a questionnaire comprising 27 4-points Likert scale items was designed. Two rounds of pilot testing and statistical analyses were conducted on the difficulty indexes, factor analysis, Spearman coefficient (flit-half method), and alpha coefficient. The result is an instrument with a degree of feasibility, validity and reliability suitable for comparative research as was found in a Spanish macro-study involving 6398 secondary school students. Preliminary results for the Spanish context are offered.