Assessment is an important tool in the learning process. This research was aimed to study Finnish as a second language (F2) teachers’ perceptions on formative assessment (FA). The data (n=208) was gathered from F2-teachers in 2015. The results show that F2-teachers use many good practices of FA in every-day work. However, many fail to find it effective and meaningful. Perceptions on assessment are quite evenly distributed in the three dimensions of assessment literacy. However, the insight on assessment is thinner in the dimensions of conceptual and praxeological knowledge compared to the socio-emotional dimension. Some assessment components align with multiple dimensions. The core concepts of FA are well known, but seldom considered advantageous. Thus, FA guidelines are not applied as intended. Further teacher education aimed for both clarifying the purpose and good practices of FA should be implemented. More research is needed especially on the role of feedback in F2-context.