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Low-income and minority students are substantially underrepresented in gifted education programs. The disparities persist despite efforts by many states and school districts to broaden participation through changes in their eligibility criteria. One explanation for the persistent gap is that standard processes for identifying gifted students, which are based largely on the referrals of parents and teachers, tend to miss qualified students from underrepresented groups. We study this hypothesis using the experiences of a large urban school district following the introduction of a universal screening program for second graders. Without any changes in the standards for gifted eligibility, the screening program led to large increases in the fractions of economically disadvantaged and minority students placed in gifted programs. Comparisons of the newly identified gifted students with those who would have been placed in the absence of screening show that Blacks and Hispanics, free/reduced price lunch participants, English language learners, and girls were all systematically “underreferred” in the traditional parent/teacher referral system. Our findings suggest that parents and teachers often fail to recognize the potential of poor and minority students and those with limited English proficiency.

Using personnel data from a large US retail firm, I examine the firm’s response to the 1996 federal minimum wage increase. Compulsory increases in average wages had negative but statistically insignificant effects on overall employment. However, increases in the relative wages of teenagers led to significantincreasesin the relative employment of teenagers, especially younger and more affluent teenagers. Further analysis suggests a pattern consistent with noncompetitive models. Where the legislation affected mainly the wages of teenagers and so was only moderately binding, it led both to higher teenage labor market participation and to higher absolute employment of teenagers.

We analyze how separations responded to arbitrary differences in own and peer wages at a large US retailer. Regression-discontinuity estimates imply large causal effects of own-wages on separations, and on quits in particular. However, this own-wage response could reflect comparisons either to market wages or to peer wages. Estimates using peer-wage discontinuities show large peer-wage effects and imply the own-wage separation response mostly reflects peer comparisons. The peer effect is driven by comparisons with higher-paid peers—suggesting concerns about fairness. Separations appear fairly insensitive when raises are similar across peers—suggesting search frictions and monopsony are relevant in this low-wage sector.

We study social interactions in the initiation of sex and other risky behaviors by best friend pairs in the Add Health panel. Focusing on friends with minimal experience at the baseline interview, we estimate bivariate ordered-choice models that include both peer effects and unobserved heterogeneity. We find significant peer effects in sexual initiation: the likelihood of initiating intercourse within a year increases by almost 5 percentage points (on an 11% base rate) if one's friend also initiates intercourse. Similar effects are present for smoking, marijuana use, and truancy. We find larger effects for females and important asymmetries in nonreciprocated friendships.

Nano-sized archaeota, with their small genomes and limited metabolic capabilities, are known to associate with other microbes, thereby compensating for their own auxotrophies. These diminutive and yet ubiquitous organisms thrive in hypersaline habitats that they share with haloarchaea. Here, we reveal the genetic and physiological nature of a nanohaloarchaeon–haloarchaeon association, with both microbes obtained from a solar saltern and reproducibly cultivated together in vitro. The nanohaloarchaeon Candidatus Nanohalobium constans LC1Nh is an aerotolerant, sugar-fermenting anaerobe, lacking key anabolic machinery and respiratory complexes. The nanohaloarchaeon cells are found physically connected to the chitinolytic haloarchaeon Halomicrobium sp. LC1Hm. Our experiments revealed that this haloarchaeon can hydrolyze chitin outside the cell (to produce the monosaccharide N-acetylglucosamine), using this betaglucan to obtain carbon and energy for growth. However, LC1Hm could not metabolize either glycogen or starch (both alpha-glucans) or other polysaccharides tested. Remarkably, the nanohaloarchaeon’s ability to hydrolyze glycogen and starch to glucose enabled growth of Halomicrobium sp. LC1Hm in the absence of a chitin. These findings indicated that the nanohaloarchaeon–haloarchaeon association is both mutualistic and symbiotic; in this case, each microbe relies on its partner’s ability to degrade different polysaccharides. This suggests, in turn, that other nano-sized archaeota may also be beneficial for their hosts. Given that availability of carbon substrates can vary both spatially and temporarily, the susceptibility of Halomicrobium to colonization by Ca. Nanohalobium can be interpreted as a strategy to maximize the long-term fitness of the host.

Using data from a large U.S. retail firm, we examine how racial matches between managers and their employees affect rates of employee quits, dismissals, and promotions. We exploit changes in management at hundreds of stores to estimate hazard models with store fixed effects that control for all unobserved differences across store locations. We find a general pattern of own-race bias in that employees usually have better outcomes when they are the same race as their manager. But we do find anomalies in this pattern, particularly when the manager-employee match violates traditional racial hierarchies (for example, nonwhites managing whites).

Mesophilic Crenarchaeota have recently been thought to be significant contributors to nitrogen (N) and carbon (C) cycling. In this study, we examined the vertical distribution of ammonia-oxidizing Crenarchaeota at offshore site in Southern Tyrrhenian Sea. The median value of the crenachaeal cell to amoA gene ratio was close to one suggesting that virtually all deep-sea Crenarchaeota possess the capacity to oxidize ammonia. Crenarchaea-specific genes, nir K and ure C, for nitrite reductase and urease were identified and their affiliation demonstrated the presence of ‘deep-sea’ clades distinct from ‘shallow’ representatives. Measured deep-sea dark CO 2 fixation estimates were comparable to the median value of photosynthetic biomass production calculated for this area of Tyrrhenian Sea, pointing to the significance of this process in the C cycle of aphotic marine ecosystems. To elucidate the pivotal organisms in this process, we targeted known marine crenarchaeal autotrophy-related genes, coding for acetyl-CoA carboxylase ( acc A) and 4-hydroxybutyryl-CoA dehydratase (4- hbd ). As in case of nir K and ure C, these genes are grouped with deep-sea sequences being distantly related to those retrieved from the epipelagic zone. To pair the molecular data with specific functional attributes we performed [ 14 C]HCO 3 incorporation experiments followed by analyses of radiolabeled proteins using shotgun proteomics approach. More than 100 oligopeptides were attributed to 40 marine crenarchaeal-specific proteins that are involved in 10 different metabolic processes, including autotrophy. Obtained results provided a clear proof of chemolithoautotrophic physiology of bathypelagic crenarchaeota and indicated that this numerically predominant group of microorganisms facilitate a hitherto unrecognized sink for inorganic C of a global importance.

Deep-sea hypersaline anoxic lakes (DHALs) of the Eastern Mediterranean represent some of the most hostile environments on our planet. We investigated microbial life in the recently discovered Lake Medee , the largest DHAL found to-date. Medee has two unique features: a complex geobiochemical stratification and an absence of chemolithoautotrophic Epsilonproteobacteria, which usually play the primary role in dark bicarbonate assimilation in DHALs interfaces. Presumably because of these features, Medee is less productive and exhibits reduced diversity of autochthonous prokaryotes in its interior. Indeed, the brine community almost exclusively consists of the members of euryarchaeal MSBL1 and bacterial KB1 candidate divisions. Our experiments utilizing cultivation and [ 14 C]-assimilation, showed that these organisms at least partially rely on reductive cleavage of osmoprotectant glycine betaine and are engaged in trophic cooperation. These findings provide novel insights into how prokaryotic communities can adapt to salt-saturated conditions and sustain active metabolism at the thermodynamic edge of life.

We evaluate a tracking program in a large urban district where schools with at least one gifted fourth grader create a separate \"gifted/high achiever\" classroom. Most seats are filled by non-gifted high achievers, ranked by previous-year test scores. We study the program's effects on the high achievers using (i) a rank-based regression discontinuity design, and (ii) a between-school/cohort analysis. We find significant effects that are concentrated among black and Hispanic participants. Minorities gain 0.5 standard deviation units in fourth-grade reading and math scores, with persistent gains through sixth grade. We find no evidence of negative or positive spillovers on nonparticipants.