Bring the class into the lab with projects set up that relate to various subcategories of the main topic you are discussing with the group. For example, in an Earth Science classroom you could have a carbon dating station, a rock classification station and a leaf identification station. Divide the class into groups, and have them move from station to station so that everyone gets to sample an activity that he is really interested in.
Assign all of your students the same project, for example a family tree that traces their lineage back at least three generations in a study of genetics. Ask each student to brainstorm a list of ways that he would like to present his family tree, such as on a PowerPoint presentation or video interviews of some members of his family. Sit down with each individual student and make a contract that states the way in which the student will complete the project. Through making a contract, the student will have some control over the style he chooses to use for completing the task.
Take the students on field trips related to the subject that they are currently studying. For example, if you are working on the human body, go to a science museum with an elaborate display on that matter. A trip to the arboretum is applicable for classes studying plant life. Another option is to take the class to a DNA research center, so that they can engage in some hands-on projects with professionals.
Bring other disciplines into your science curriculum to target students who are interested in those courses. For example, take the students outside and have them write down the characteristics of rocks, leaves or other parts of natural. They can write haiku poems or songs based off of the characteristics of the objects. Incorporate art by having students use strips of paper to create a chain link representative of DNA. Or they could draw a cartoon or create a poster board that illustrates the cycles that animals or plants go through in their lives.