The questions in the practice assignments given to students in the form of worksheets or other formats are often grouped by chapter, topic, or concepts. There is a great emphasis on categorization. Most of the end-of-chapter problems in chemistry textbooks are organized by sections. Although this was done with the intention of helping students navigate the assignments more easily and practice in order, it is not what they are expected to do during the tests. There is a mismatch between what they practice on and how they are tested. The goal of this study is to examine the influence of the structure of the assignments on students’ problem-solving performances. Two groups of students from chemistry classes were recruited to participate in this study. Each group had the same length of practice and identical questions with only one difference. The experimental group had assignments with mixed organization of questions, while the control group had traditional assignments with the questions organized around chapters and topics. Students completed three two-hour long problem-solving sessions during the weekends. Evaluation of their progress consisted of their solutions obtained from one pre-test and three post-tests, with one given after each problem-solving session. The study revealed that students in the experimental group increased their problem-solving success more than those in the control group starting from the first intervention. The achievement gap widened as the study progressed. It is recommended that educators and textbook publishers create and utilize assignments that contain more mixed questions on different topics and chapters.