To promote computational thinking (CT) education in primary schools, in-service teachers need to attend CT teacher development programmes. One of the intended learning outcomes of the programme is to improve CT practices of teachers, which is one of the three key elements in the CT framework proposed by Brennan and Resnick. Assessing one's CT practices is challenging because there is no universally agreed-upon assessment method on CT practices in the existing literature. This study adopted the Evidence-centered Assessment Design (ECD) method to design test questions to evaluate teachers' development of CT practices. This study provided two Teacher Development Courses (TDCs) to enable teachers to teach CT through programming. TDC 1 focused on developing CT concepts, practices and perspectives of teachers, while TDC 2 put emphasis on pedagogies of teaching CT. 80 teachers participated in the two courses. The CT practices tests were administered before the courses, between the two courses and after the courses respectively. Results indicated that CT practices were improved progressively when the in-service teachers attended the two courses. It indicated that it is useful for teachers to experience programming practices in their initial learning as well as during their pedagogical development.