The article draws on posthumanist theorizing to critically inquire into and thereby specify the relational ethics ingrained in the dialectical praxis co-research approach of psychology from the standpoint of the subject (PSS). It departs from problematizing power imbalances manifest in participatory research with children, and argues that attempts to question the child/adult binary via the concept of ethical symmetry have failed to address this binary’s entanglement with power imbalances propelled by the researcher/researched as well as the human/posthuman binaries. In contrast, PSS’ co-research ethics, implicit to the concepts of conduct of everyday life and conflictual cooperation, clearly attends to the researcher/researched binary, but has little attended to the child/adult or the human/nonhuman binaries in explicit ways. Therefore, the article discusses how the posthumanist quest for fundamentally questioning human exceptionalism may inform psychological praxis co-research, by radically opening its inquiries up for ongoing renegotiations of deadlocking categories. It invites to co-explore what it means to be part of this world across all conceivable binaries. Implicitly, PSS already shares two central tenets with this posthumanist ethos of diffraction: its co-research strives for indeterminate and caringly speculative becomings, and it does so via the collective engagement in difference-enacting knowledge praxis. Finally, it is suggested that the concept of teleogenetic collaboration, as a specification of PSS’ co-research methodology, explicates these tenets. The concept calls for continuously finding out about one another’s knowledges and directionalities for future action from within everyday life, across all vital forces and across dialectical-materialist and new materialist theorizing.