Would you like to challenge your middle school students to explain a range of phenomena-- from how nylon thread can form from two clear, colorless liquids to how a snake that eats only eggs can make body structures such as skin and scales that don't look anything like an egg? Would your students enjoy building molecular models to understand how an herbicide prevents weeds from growing? If so, then Toward High School Biology is the curriculum for you. This 19-lesson unit helps students connect core ideas about chemical reactions to the biological phenomena of growth and repair in plants and animals. Students first investigate easily observed changes in physical science contexts, such as the rusting of a metal bicycle. Then, they explore more complex changes that take place inside living organisms, such as the production of human muscles. Legos, ball-and-stick models, videos, and a variety of print manipulatives help students grasp the underlying science principles. Developed by a team of scientists and science educators, Toward High School Biology was field tested extensively. Results show that students who used the unit had significant learning gains compared with students who used other materials. The unit's lessons support the Next Generation Science Standards and integrate all three dimensions of science learning, with a strong emphasis on supporting students in developing evidence-based explanations. The goal of the unit is to help students overcome many common conceptual difficulties and provide the foundation in biochemistry that students will need for high school biology and beyond.