Abstract: Fifty-nine primary mathematics teachers of three intakes participated in in-service training in alternative assessment newly offered at a university in Singapore. A study, action research in nature, was undertaken to examine the effects of the in-service training and investigate relevant issues in promoting teachers' use of alternative assessment in classrooms. Data were mainly collected through questionnaire surveys, the participants’ work on an authentic alternative assessment task, and field-notes of the training. The results indicate that systematic training in alternative assessment is highly needed for school teachers, and in-service training can be an effective way to promote their professional growth in this area, especially through their integrating authentic alternative assessment tasks into their actual classroom teaching as part of the training. In addition, the study reveals that the current school curriculum does not well reflect the new development of assessment and therefore there is a need to integrate the concept and content of alternative assessment into school curriculum to facilitate teachers’ use of alternative assessment in classroom. Some other relevant issues, including advantages and disadvantages of in-service training, are also documented in the article.