Mobile devices have become a learning tool with great potential in both formal and informal learning; however, mobile learning readiness research in school education is relatively limited. This study investigated teachers' readiness to adopt mobile learning in K-12 classrooms. A questionnaire was administered to 920 teachers in Greece and four factors were extracted, "Possibilities," "Benefits," "Preferences" and "External influences." Teachers, in general, expressed positive perceptions on mobile learning readiness. The highest percentage of agreement regarded the possibilities of mobile learning (over 60%). ICT training and attendance of ICT conferences, both affected positively teachers' perceptions on mobile learning benefits and preferences. Teachers who use mobile devices in class reported significantly more positive perceptions on all factors, while gender or age had no impact on perceptions. There was a higher probability of mobile devices' usage in class among teachers working in elementary schools (in comparison with those working in high schools or general/vocational lyceums). Stronger perceptions on mobile learning benefits, preferences and external influences were associated with an increased likelihood of using mobile devices in the classroom. Teachers' readiness perceptions can be explored from a multi-dimensional perspective, and also be associated with mobile technology use in classrooms. Implications for teacher professional development, methodology and pedagogical practice are discussed.