Teacher self- and collective efficacy are important motivational factors in determining teachers' effort in their professional practice. Teachers' higher levels of self- and collective efficacy are positively associated with student achievement in specific domains, and teachers' enhanced wellbeing and commitment to their profession. This qualitative study explores primary teachers' own views about naturalistic and characteristic experiences and influences that have strengthened and weakened their efficacy in teaching reading. Five themes of naturalistic sources of enhancement in self- and collective efficacy are identified that are consistent with predictions of Bandura's social cognitive theory and studies involving interventions in schools by expert trainers. The themes are combined into a model of growth in teachers' efficacy and can potentially inform decision-making in schools in supporting and enhancing teachers' self- and collective efficacy when teaching reading.