Blogs and journals don't publish enough `negative' results (cases where we fail to reject the null hypothesis). So I'll start with a paper I recently skimmed through:
In this paper, we analyze how the share of immigrant children in the classroom affects the educational attainment of native Dutch children. Our analysis uses data from various sources, which allow us to characterize educational attainment in terms of reading literacy, mathematical skills and science skills. We do not find strong evidence of negative spill-over effects from immigrant children to native Dutch children. Immigrant children themselves experience negative language spill-over effects from a high share of immigrant children in the classroom but no spill-over effects on maths and science skills.The authors rely on differences in immigrant class shares within schools (i.e. they used school fixed effects), and also show that there are no observable differences in the allocation of resources between these classrooms - a standard objection would have been that head teachers may have allocated more resources to immigrant-heavy classrooms, although the authors show that these classrooms don't receive any observably different teaching inputs (materials, teacher quality, etc is no different for these classes).
Also interesting is a result that while there appear to be no peer effects of immigrants on non-immigrants, immigrant children are helped by the presence of other immigrants in science and math, but hindered in language.