Unlike the summary that attempts an objective rendering of the key points in a reading, an annotation typically asks students to note key ideas and briefly evaluate strengths and weaknesses in an article. In particular, annotations often ask students to note the purpose and scope of a reading and to relate the reading to a particular course project.
You can have students annotate (and eventually compare) readings assigned for the class, or you can ask students to compile annotations to supplement the course readings. Each student's annotations can be distributed to the class in one handout or through electronic media (Web forum, e mail).