Decades of research has assessed the benefits of children's and adolescents' friendships, but friendships among youth often dissolve within a matter of months or years. Studies have investigated predictors and consequences of friendship stability with the expectation that, in order for friendships to have a positive or negative influence on youth,…

This paper focuses on commonalities and differences of three approaches to large-scale professional development (PD) in mathematics education, based on two studies from Germany and one from the United States of America. All three initiatives break new ground in improving PD targeted at educating "multipliers", and in all three cases…

Research and scholarship into educational effectiveness research (EER) is comprehensively reviewed from the UK, The Netherlands, the US, Cyprus, Belgium, Sweden, France, Germany, New Zealand, Australia, and other societies, dating from the field's origins in the 1970s. Issues include its history, methodological and theoretical advances, scientific…