Teachers feel inadequate to face pupils' behavioural problems in schools, yet teachers are expected to play significant roles in providing and supporting pupils' appropriate social behaviour. Unfortunately, teacher education in Finland and globally seems to offer little content for behavioural support, and in-service training sessions are filling this educational gap. The key context in this study is the in-service training that was directed at primary school teachers and teaching staff. The aim of this study was to explore the efficacy of short-term in-service training and discuss the support that in-service training can provide for behavioural problems that are experienced in school. From 2017 to 2021, over 200 teachers or teaching staff members participated in check-in, check-out (CICO), in-service training sessions that were funded by the Finnish National Agency of Education and organised by the Niilo Mäki Institute. Afterwards, the participants were asked to answer a questionnaire concerning their use of the CICO model in their own schools. The post-training questionnaire reached over 80 participants. The results indicated that CICO support was introduced well to schools after the training; however, for some teachers, the short in-service training did not sufficiently support this implementation. Also, factors that complicated and contributed the implementation were examined. According to the results of the study, implementation can be supported with active learning, e.g. opportunities to practise new skills and the use of models.