If a student writes two essays, the score reliability can be estimated from the correlation between the essays. However, if the essays are in different modes or require different skills, the reliability may be underestimated from the correlation. In Advanced Placement Program® history examinations, students wrote one standard essay and one essay that required analysis and synthesis of historical documents that were included with the question statement. If these document-based questions (DBQ) were assessing substantially different skills from the standard essays, then the reliability of the DBQ scores would be underestimated from their correlation with a standard essay score. A sample of 1,045 U.S. history students and 891 European history students participated in a special study in which they wrote essays for either two DBQ questions and one standard essay question or three standard essay questions. The DBQ correlated as highly with a standard essay as with another DBQ, suggesting that the simple correlation of the two types of scores did not underestimate the reliability of the essay scores.