You form an impression of a student within five seconds of seeing them. This impression is likely to stick  even after you interact with them for a while (Ambady et al., 2020). While that thin slice of behavior may or may not provide an accurate read of them, that impression you form and the expectations that stem from it can influence how THEY learn! Think poorly of them, and they could learn poorly. Outcomes could be even worse if you have biases.