Teach For America (TFA) Teach For America (TFA) recruits and selects graduates from some of the most selective colleges and universities across the country to teach in the nation's most challenging KϪ12 schools throughout the nation. TFA has grown significantly since its inception in 1990, when it received 2,500 applicants and selected and placed 500 teachers. In 2005, it received over 17,000 applicants and selected and placed a little over 2,000 new teachers, and the program anticipates expanding to over 4,000 placements in 2010. In total, the program has affected the lives of nearly 3 million students.The growth of the program suggests that TFA is helping to address the crucial need to staff the nation's schools, a particularly acute need in high-poverty schools, but TFA is not without its critics. The criticisms tend to fall into two categories. The first is that most TFA teachers have not received traditional teacher training and therefore are not as prepared for the demands of the classroom as traditionally trained teachers. TFA corps members participate in an intensive five-week summer national institute and a two-week local orientation and induction program prior to their first teaching assignment.1 The second criticism is that TFA requires only a two-year teaching commitment, and the majority of corps members leave at the end of that commitment. The short tenure of TFA teachers is troubling because research shows that new teachers are generally less effective than more experienced teachers (Rivkin, Hanushek, & Kain, 2005;Rockoff, 2004).The research reported here investigates the relative effectiveness (in terms of student tested achievement) of TFA teachers and examines the validity of the criticisms of TFA. Specifically, we look at TFA teachers in high schools, and especially in math and science, where considerable program growth is planned over the next few years. To the best of our knowledge, this is the first study of TFA at the high school level. Using individual-level student data linked to teacher data in North Carolina, we estimate the effects of having a TFA teacher compared to a traditional teacher on student performance. The North Carolina data we employ are uniquely suited for this type of analysis because it includes end-of-course (EOC) testing for students across multiple subjects. This allows us to employ statistical methods that attempt to account for the nonrandom nature of student assignments to classes and teachers, which have been shown to lead to biased estimates of the impact of teacher credentials (Clotfelter, Ladd, & Vigdor, 2010;Goldhaber, 2007). Making a Difference? The Effects of Teach For America in High SchoolThe findings show that TFA teachers are in general more effective, as measured by student exam performance, than traditional teachers. Moreover, they suggest that the TFA effect, at least in the grades and subjects investigated, offsets or exceeds the impact of additional years of experience, implying that TFA teachers are at least as effective as experienced hi...

This paper reports two studies that measured the effects of different "video skim" techniques on comprehension, navigation, and user satisfaction.Video skims are compact, content-rich abstractions of longer videos, condensations that preserve frame rate while greatly reducing viewing time. Their characteristics depend on the image-and audio-processing techniques used to create them. Results from the initial study helped refine video skims, which were then reassessed in the second experiment. Significant benefits were found for skims built from audio sequences meeting certain criteria.

Quick access to short, relevant video segments enables efficient use of a digital video library. This study evaluated an interface designed for such access, an interface that allows the user to browse a set of segments generated by a search query. Subjects' performance and attitudes were measured while they performed a fact-finding task to determine the relative effectiveness of three presentations: a text list, naively chosen visual imagery, and querybased visual imagery. Results show little difference in performance and subjective satisfaction between text lists and naively chosen imagery, but significant improvements when the images that represent video segments are based on the query that returned the segments (query-based poster frames). This result applies to the organization and representation of information in digital video libraries.

Multimedia abstractions form essential components of digital video libraries because they enable a user to determine a video's distinguishing content without investing long viewing times or requiring high networktransfer speeds. This paper presents usage and evaluation data for abstractions implemented the Informedia Digital Video Library, and discusses implications for video delivery over the Web. Keywords