The effect of immigrant concentration in schools on native and immigrant children's reading and math skills

Using a unique and very rich PISA dataset from Denmark, we show that the immigrant concentration in the school influences reading and math skills for both immigrant children and native children. Overall, children in schools with a high immigrant concentration score lower on reading and math test scores. The negative effects associated with attending a school with a high immigrant concentration are fairly robust across estimation methods. IV estimates, taking into consideration that parental sorting across neighborhoods might bias the OLS estimates, indicate that immigrant concentration in schools is still important in determining children's math test scores. The estimates are less precise regarding the effect of immigrant concentration on reading test scores. The immigrant concentration in the school has a stronger effect for native children than for immigrant children, but the differences are more pronounced for the math test.     

A cognitive gap between arithmetic and algebra

Serious attempts are being made to improve the students' preparation for algebra. However, without a clear-cut demarcation between arithmetic and algebra, most of these undertakings merely provide either an earlier introduction of the topic or simply spread it out over a longer period of instruction. The present study investigates the upper limits of the students' informal processes in the solution of first degree equations in one unknown prior to any instruction. The results indicate the existence of acognitive gap between arithmetic and algebra, a cognitive gap that can be characterized asthe students' inability to operate spontaneously with or on the unknown. Furthermore, the study reveals other difficulties of a pre-algebraic nature such as a tendency to detach a numeral from the preceding minus sign in the grouping of numerical terms and problems in the acceptance of the equal symbol to denote a decomposition into a difference as in 23=37–n which leads some students to read such equations from right to left.This research was funded by the Quebec Ministry of Education (Fonds FCAR-92-ER-1032).The authors wish to thank Patricia Lytle for her many helpful suggestions in the preparation of this paper.     

Rabbit nictitating membrane conditioning: Lower limit of the effective interstimulus interval

In three experiments, the nictitating membrane response of rabbits was conditioned for 10 daily sessions at interstimulus intervals (ISIs) ranging from 48 to 125 msec, followed by a shift to 250 msec for 5 days. At tested ISIs shorter than 67 msec, there was no evidence of conditioning, and postshift performance revealed neither facilitation nor interference as a result of the first 10 conditioning sessions. Postshift performance of groups conditioned at preshift ISIs of 67 msec or longer revealed a gradient of increasing savings with increasing ISI. One of the groups in Experiment 1, initially conditioned at 250 msec ISI and then shifted to 48 msec, exhibited extinction of the previously well-conditioned response. Analysis of CR-onset latencies substantiated the absence of associative effects at very short ISIs. It was concluded that there is a temporal limit below which classical conditioning of the nictitating membrane response of rabbits employing forward CS-US pairing does not occur.     

‘Libre’ software: turning fads into institutions?

The article presents an economic analysis of Libre software and of its sustainability as a new economic model for software. We underline the role of Libre software development communities and analyze incentives for both kernel and obscure developers. We emphasize the role of the so-called ‘public’ licenses to provide an appropriate institutional framework. We show that several features of Libre software also allow it to improve faster than proprietary software, and therefore to achieve strong market performance when competing against existing standards, even when proprietary software producers react. We illustrate our point using a simple local and global interaction model to study the technological competition between Linux and Windows on the server operating system (OS) market. We finally argue that if sufficient initial momentum could be created through public intervention Libre software could turn from a fad into an efficient economic institution to correct inefficiencies due to network externalities.