Sharing ideas can strengthen students’ science explanations. Yet, how to guide uses of peers’ ideas, and what the impacts of those ideas are on students’ learning, are open questions. We implemented a web-based cell biology unit with 116 grade 7 students, and explored how peers’ ideas are used during explanation building, and how prompts to draw on peers to either diversify or reinforce existing ideas impacted the quality of students’ written explanations. Among other findings, exchanging ideas with peers led to all students improving their explanation quality upon revision; and students prompted to diversify their ideas showed greater learning gains by the end of the unit, while students prompted to reinforce ideas, who used more peer-generated ideas in preparation to write their explanations, produced higher quality explanations. This study builds our understanding of the influence of peer ideas on learning, and offers insight into supporting students in engaging effectively with peers’ ideas.

BABAR, the detector for the SLAC PEP-II asymmetric e+e- B Factory operating at the γ(4S) resonance, was designed to allow comprehensive studies of CP-violation in B-meson decays. Charged particle tracks are measured in a multi-layer silicon vertex tracker surrounded by a cylindrical wire drift chamber. Electromagnetic showers from electrons and photons are detected in an array of CsI crystals located just inside the solenoidal coil of a superconducting magnet. Muons and neutral hadrons are identified by arrays of resistive plate chambers inserted into gaps in the steel flux return of the magnet. Charged hadrons are identified by dE/dx measurements in the tracking detectors and by a ring-imaging Cherenkov detector surrounding the drift chamber. The trigger, data acquisition and data-monitoring systems, VME- and network-based, are controlled by custom-designed online software. Details of the layout and performance of the detector components and their associated electronics and software are presented. © 2002 Elsevier Science B.V. All rights reserved.