Lecture as little as possible. Education research demonstrates how little students retain information from lectures. Instead of lecturing, ask students questions about the natural world and wait for students to answer. Nevertheless, students require historical context or an understanding of how scientific discoveries developed and built off each other, so provide background information.
Divide the class into small groups "to get acquainted with the things around them --- including devices, organisms, materials, shapes, and numbers --- and to observe them, collect them, handle them, describe them, become puzzled by them, ask questions about them, argue about them, and then to try to find answers to their questions" (Science for All Americans Online). High-achieving students need "varied opportunities for collecting, sorting and cataloging; observing, note taking and sketching; interviewing, polling, and surveying; and using hand lenses, microscopes, thermometers, cameras, and other common instruments. They should dissect; measure, count, graph, and compute; explore the chemical properties of common substances; plant and cultivate; and systematically observe the social behavior of humans and other animals. Among these activities, none is more important than measurement, in that figuring out what to measure, what instruments to use, how to check the correctness of measurements, and how to configure and make sense out of the results are at the heart of much of science and engineering" (Science for All Americans Online). In addition, good students can tutor or teach struggling students which reinforces their knowledge.
Assign as many activities as possible that develop writing and speaking abilities such as note taking from observations, writing lab reports, writing essays in which students take a stance on a scientific controversy and making critiques of classmates' reports. Writing develops critical abilities.
Assign independent research projects that give accelerated students freedom to do more complex and challenging assignments than the norm. Upon completion, students should have a public exhibition of their experiments, findings or discoveries.