Research has shown that formative assessment is a key ingredient in raising student achievement. The goal of formative assessment is not to grade students, but to pinpoint where they are having trouble and then to take appropriate instructional action. In a review of 250 studies, Black and Wiliam found that formative assessments had a more significant effect on student achievement than practically any other classroom innovation. However, effective formative assessments must provide insight into student thinking, something multiple-choice tests don't do very well, as well as allowing for quick evaluation, the Achilles' heel of document-based questions (DBQs). Designing such assessments was the authors' challenge and their opportunity. With support from the Library of Congress Teaching with Primary Sources Program, they set out to marshal the resources of the digital revolution to create new history assessments. How could they use the Library's vast collection of documents, photos, paintings, speeches, radio broadcasts and film clips to help teachers track students' growth as thinkers? In partnership with the San Francisco (California) Unified School District and the Lincoln (Nebraska) Public Schools, their research group has spent nearly three years constructing, piloting, and revising assessments that provide social studies teachers with new options. They call their items "History Assessments of Thinking" (HATs). HATs fill the void between the recall of discrete facts on a multiple-choice question and the complex orchestration of skills required by a document-based essay. They have piloted dozens of HATs with thousands of students in California, Nebraska, Florida, Iowa, Wisconsin, and as far away as Singapore, while also conducting validity studies in which they ask students to tell them what they are thinking as they complete their assessments. The results have been promising. Evidence suggests that their items do indeed tap important aspects of historical thinking. Just as promising is feedback from teachers, who report that HATs give them the kind of information they need to make adjustments in their teaching. (Contains 11 notes.)