This paper illustrates a 5-year case study (2007-2012) of a course in Environmental Science Education designed for the training of practicing Greek in-service elementary teachers. The aim of the study was to reveal teachers' views towards the course they attended, which was designed on the basis of inquiry principles. This was achieved through an assessment of the course by the 82 participants. The responses of the teachers to 4 open-ended questions were analyzed using content analysis. Results revealed that in-service elementary teachers found the course well-organized and commented favorably for their active participation and group working, the field study, the hands-on experiments and the software used. They would prefer to have more time available for their activities, smaller range of topics and simpler equipment. In general, favorable comments indicate a positive attitude for the course and a successful implementation on behalf of the lecturers while critical comments and suggestions for improvement constitute essential guidelines for the development of similar teacher training courses in the future. Challenges in developing similar courses include the teachers' lack of knowledge in Environmental Science and teachers' need for practical work.