This study examined the effects of cooperative and individual weblog-integrated writing instruction on the writing performance of 5th grade students. A mixed methods approach was used, including a quantitative pre-test post-test experimental design and qualitative case study. 21 students were divided into an experimental group that used cooperative weblogs (n=12) and a control group that used individual weblogs (n=9). Both groups received writing instruction based on blended learning. Results showed no significant difference in writing performance between the groups, except for ideas/content where the individual weblog group performed better. Qualitative findings suggested feedback had a positive effect on writing, while cooperative learning had a negative effect.