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Ecologists construct physical microcosms that exemplify mechanisms and relations in ecosystems. This poster describes how a 7th-grade classroom complemented field study of an intertidal ecosystem with design of classroom microcosms. Initial designs appeared constrained by literal resemblance. As students’ inquiry increasingly focused on interactions among organisms, they configured microcosms to facilitate observation of these interactions. Microcosms became sites for studying processes that could be inferred from field data but rarely observed directly. 

The work of ecologists entails structuring variability by parsing random and directed variability. Middle-grade students are often introduced to ideas about probability and statistics in mathematics, but these ideas are rarely employed in science investigations. This paper reports on a design study in one 7th-grade science classroom that participated in a citizen-science project investigating changes in invasive crab populations. Students surveyed crab abundance at one field site, contributing observations to a citizen-science database. Finding an unexpected atio between male and female crabs in their sample, students compared the ratio obtained in the field to a simulated sampling distribution of ratios in light of an equiprobable assumption. Finding that their sample’s sex ratio was improbable yet consistent with samples in the larger database instigated a search for ecological mechanism. Evidence of student thinking in classroom conversations point to seeds of distinguishing random from directed variability.