Web-based training gains popularity due to the pervasiveness of Web applications, abundant hyper media contents, and other attractive attributes. However, previous experience and research indicate that learners in Web-based learning environments tend to drop out when they lose orientation or have insufficient interaction with support providers during self-directed learning process. Formative assessment activities can not only identify weakness of learners, but also can provide guidance toward ultimate learning goals through interactions with learners. Various instructional resources have been designed to enrich e-learning context, and most of these resources are integrated proprietarily within Web-based learning platforms. The service oriented approach, which enables a more flexible way for architecting software systems, could be applied in a variety of domains, including those with the purpose of pedagogy. This research work aims to investigate a method of enhancing interactivity in Web-central learning environments by means of blending formative assessment services into instructional processes. A proof-of-concept prototype has been implemented and the preliminary usage shows that the interactions between self-directed learners and support-providers are critical to sustaining those learners as well as better learning achievements.