Will students get covid-19 if everyone in their classroom is wearing a mask, but desks not so far; not crowded?

This is tough to answer because mask protection varies with the type of mask used and how well it fits. For example N 95 (very good) versus cloth mask (ok but not great). Masks must also cover BOTH the nose and mouth. Other hygienic issues such as hand washing and cleaning of desktops and doorknobs for example also play a role in transmissibility of COVID-19. So masks alone help but are not 100%.

Studies on cloth masks reveal failure to protect from airborne droplets, and MIT studies conclude that in absence of effective ventilation inside, that eventually a viral infection will diffuse widely with or without masks. N-95 are the most effective, but also most restrictive. Sorry, but this entire area is controversial, and hard to be certain about much of this. Discuss locally with your Dr