Assessment is a key aspect within teaching and learning processes in higher education (Torrance, 2007). Formative assessment may be viewed simply as constructive feedback to support learning or more holistically as ongoing assessment based on sustained engagement in learning activities within a supportive social context that expand teachable moments to scaffold learning. Online education now pervades higher education worldwide but effective ways to incorporate formative assessment within online settings is not well understood. Previous research in online postgraduate courses designed for teachers as professional learners illustrate that engagement with authentic learning activities promotes meaningful learning and transferability to their communities of practice (COP) (e.g. Mackey, 2011). However, there appears to be paucity of literature with a focus on assessment in professional learning. This thesis explores formative assessment within online postgraduate courses designed for teachers as professional learners who aim to develop capacity to incorporate information communication technologies (ICT) in their own practice. Case studies are presented to richly illustrate the design, implementation and evaluation of the effectiveness of two courses; and then further re-examined to elucidate strategies and key characteristics that can foster (or hinder) online formative assessment. Authentic and developmental learning perspectives underpinned by situated cognition theory framed the design and interpretation within a multiple-case methodology. Evidence of experiences and perceptions of the teachers and their professional students included online observation, analysis of the discourse, and semi-structured interviews. An authentic learning environment that sustained productive engagement is illustrated in both case studies along with many techniques that the teachers designed to underpin formative assessment. A key characteristic in both courses was the design of authentic assessment activities that are relevant and meaningful in real-life contexts. Techniques identified included appropriate learner autonomy, and opportunities to negotiate shared understanding of learning goals and expected outcomes including the sharing of student-created artefacts. The online reification of the artefacts and other learning community support was enabled by the ongoing documentation through creative use of online discussion forums as a feature within the learning management system (LMS). These techniques enriched the processes of ongoing monitoring, assessment of evidence of learning and interactive formative feedback. Both teachers’ beliefs about self and peer feedback also enabled both teachers to design for productive synergies between formative and summative assessment that promoted engagement and deep learning. Additional synergies of discourse among peers related to immediacy, interactivity, and mutuality in which the students recognized themselves and valued their peers as source of constructive feedback. The students also demonstrated meaningful reflectivity that manifested reflexivity within the context of their professional practices. Online formative assessment is illustrated in both courses as a form of collaborative engagement in authentic learning, including assessment activities with opportunities for ongoing interactions and formative feedback. The open-ended authentic assessment activities supported professional learners to connect the online discourse to their own classroom practices, as well as keenly engage with authentic projects that are situated in their schools. Learner autonomy stimulated self-regulated learning in which students went beyond achievement of the expected learning outcomes for summative assessment to engaging with tasks and processes that matched their own learning goals, interests and contextual needs. Learners’ involvement within formative assessment processes enhanced opportunities to negotiate meanings which fostered shared authenticity.The inherent authenticity in the course design also stimulated application of prior knowledge and experiences in ways that promoted meaningful learning. Engagement in asynchronous dialogue as a community of learners with shared goals and practice elicited alterative perspectives and disorienting dilemmas. This stimulated learners to think in new ways and more critically and to develop relevant professional competencies in ICT. These in turn supported teachers as professional learners to confidently apply their developing pedagogical practices with ICT in their own classrooms; and to share those with school colleagues. This study illustrates ways that online formative assessment can be designed to support learners to develop relevant knowledge and professional skills that increase professional competencies. Incorporating authentic formative assessment in the course design also impacted teachers’ continuing professional development (CPD), and thus their schools. A key finding from this research is conceptualization of formative assessment as a collaborative pedagogical strategy in which both the teacher and students are active players. This research provides evidence that innovative integration of formative assessment in online settings can support committed professional learners to develop competencies that are transferable into their own practice. This suggests that ongoing formative assessment is an important strategy to increase the quality of online professional development in many fields, in addition to that of education.