In this paper we present a newly developed online learning platform which introduces gamification elements into software engineering education. Starting from assumptions based on cognitive load theory we present the design of an online gamification-based training system to be used in software engineering contexts. Students can voluntarily solve challenges for which they may earn credits. These small problems serve as assessments; the approach follows the assessment for learning paradigm in that assessments provide formative feedback to enhance the learning experience. The combination of formative assessment and gamification is new to software engineering education. We describe system design as well as the different types of challenges in detail. We also provide several examples for actual challenges used in an object-oriented programming introduction using Java.