This study responds to the Italian Ministry of Education mandate that, starting the 2013-2014 academic year, CLIL be implemented in the "final" year of high school, during content time, by content teachers with C1-level competence in English. This decision raises numerous concerns, at least in Calabria: most content teachers have, at best, B1-level English competence and consider CLIL the final straw in an overburdened scholastic curriculum. Secondly, EFL teachers without sufficient content competence are reluctant to contribute to CLIL initiatives, seeing themselves reduced into "walking (technical) dictionaries." Content-driven task-based activities were therefore developed to enable both the EFL teacher (Grandinetti) to work within her comfort zone on an advanced-level science topic and an experienced science teacher (Langellotti), with "only" B1-level English-competence, to fulfil the L1-science curriculum. Such "professional limitations" prompted the development of CLIL activities which necessarily scaffold between "comprehensible language" and "accessible content", transforming teacher-centred lecturing into learner-centred learning. The materials used and the theories guiding their development are presented, alongside analyses of classroom discourse. Positive learning outcomes were obtained and more importantly, maintained, especially from normally disaffected students. Since the sub-optimally bilingual reality of Calabria may reflect many international contexts, delineating how content and language teachers "can CLIL" within their comfort zones will ensure that CLIL contributes successfully to international mainstream bilingual education. (Contains 4 tables, 7 figures and 3 notes.)