In this article, an instrument for assessing upper secondary school students' levels of technological literacy is presented. The items making up the instrument emerged from a previous study that employed a phenomenographic research approach to explore students' conceptions of technology in terms of their understanding of the "nature of technology" and their "interaction with technological artefacts." The instrument was validated through administration to 1,245 students on completion of their 12 years of formal schooling. A factor analysis was conducted on the data and Cronbach alpha reliability co-efficients determined. The results show that a five-dimension factor structure (namely, "artefact," "process," "direction/instruction," "tinkering," and "engagement") strongly supported the dimensions as developed during the original phenomenographic study. The Cronbach alpha reliability co-efficient of each dimension was satisfactory. Based on these findings, the instrument has been shown to be valid and reliable and can be used with confidence.