Effective writing activities can help students learn any type of content better. I found a great list of resources from Ohio State University on incorporating writing into lesson plans. I could see these being engaging activities for class wikis, blogs or even student journals.
By incorporating informal writing into your course (as an in-class activity or as homework), you can help students come to a deeper understanding of the course material and you can gain insight into what you students are (and are not) learning.
OSU Writing Across the Curriculum Resources
Reflective Writing: Applying Key Terms/Concepts to Personal Experience – To help students understand and apply course concepts, you can have them complete short informal writing assignments…in which they take a key term or idea from their reading and relate it to their personal experience.
Reflective Writing: Analyzing (and Preparing to Discuss) Readings– Students will often be much more vocal and active in discussion if they are prepared. To ready students for discussion, you can have them complete informal reading responses. Depending on your course goals, these reading responses might entail summarizing, analyzing, and/or posing potential discussion questions.
Passing Notes in Class– This activity offers an informal writing opportunity for students to identify, interrogate, and develop things they did and did not understand about the content of the course. Before the beginning of class, ask every student to post a question or write a note asking about some aspect of the course about which they are unclear. You can pair students up to answer questions, use the questions as a jumping off point for class discussions, or post supplemental materials based on questions students raise.
Designing Supplementary Materials – There are a number of different supporting materials students have learned to use for studying. Encourage them to prepare or share these materials with the class. Possible materials include: flashcards on terminology, registered objections (things they were not able to say during the course discussion but later felt they should have), summaries or analyses of class discussions, pretend quizzes, quote lists, page reference guides, notes, and so on.
Believing and Doubting – This activity is a good way to get students to move beyond simple “either/or” binaries in their reading. Ask students in small groups (or as an individual informal writing activity) to identify the main thesis of a course reading and to outline 3 reasons they believe it and 3 reasons they doubt it. In this way, you can jumpstart discussion and encourage students to think more analytically and complexly (rather than just going with their gut reaction).
Additional Writing Resources:
Writing Across the Curriculum: Activities for Any Content Area
Reading and Writing Across the Curriculum tips
Samples and Suggestions for Informal Out-of-Class Writing Assignments