The purpose of this study is to investigate the effects of self-assessment in writing in the Swedish subject. This has been done through the research questions, “how does the pupils’ handling of language rules and formalities change during self-assessment?”, as well as “how does it affect the teacher’s conditions to assess pupil texts if the pupils’ carry out/completed self-assessment?”. The study’s theoretical starting point has been the socio-cultural perspective and the concepts of “mediation”, “artefacts” and “appropriation” have been the basis for analysis of the results. The study has been conducted through a Lesson study where two different teaching arrangements were carried out, at two different schools in two different grades. Both classes had to complete a lesson in writing where self-assessment was not used, and then to conduct a lesson where self-assessment was carried out by having pupils use checklists to self-assess their own texts. The results from the two different teaching arrangements were then compared with each other.

The result shows that self-assessment through the checklist raised the quality of the pupils’ texts when it comes to handling language rules and formality. Overall, 27 out of the 32 pupils made fewer errors in the lesson where the checklist was used. A total of 149 errors were made in the lesson without a checklist and 64 errors in the lesson where the checklist was used. The results show that the checklist could function as a supplement to the teacher’s assessment regarding language rules and formality, but cannot be considered to replace this assessment entirely. On the other hand, the lower number of errors the pupils make with the help of the checklist can cause the teacher’s conditions to change, as the teacher needs to spend less time on just this.