This paper regards a study aiming to investigate junior high school pupils' attitudes and self-efficacy of using mobile devices. A 25-item questionnaire was administered to 260 pupils aged 12-15 years old, in Greece. Pupils' attitudes were positive, and four factors were extracted, "perceived usefulness", "affection", "perceived control" and "behaviour". Regarding pupils' self-efficacy, one factor was revealed and this was significantly correlated with all attitude factors. Most of the pupils (over 87%) expressed high self-efficacy in using mobile devices. Higher self-efficacy was linked to positive perspectives and feelings, to greater willingness to use mobile devices, and to favorable perceptions towards their independent control. It is suggested to describe pupils' attitudes of using mobile devices with respect to discrete dimensions. Gender or age differences in attitudes were very small. The mobile devices attitudes and self-efficacy questionnaire is suggested to be used with other adolescent populations of different countries, in order to reveal possible similarities and differences.