In a typical laboratory setting, a reaction is carried out in a ventilated hood with air circulation provided by outside air. a student noticed that a reaction that gave a high yield of a product in the winter gave a low yield of that same product in the summer, even though his technique did not change and the reagents and concentrations used were identical. what is a plausible explanation for the different yields?

The reaction is exothermic

Explanation:

The phenomenom described can be a result of an exothermic reaction.

Chemical reactions offen exchange energy with the enviroment, they can either:

Following the principles of Le Chatellier, the first ones will be benefited by low temperatures, because the reaction will try to reverse that and move the equilibrium to the products (releasing heat).

On the other side, endothermic reactions will be benefited by high temperatures  because the reaction will try to reverse that and move the equilibrium to the products (absorbing heat).

Being all that said, the behavior described is the one of an exothermic reaction: having a higher yield in low temperatures (winter) than in high temperatures (summer).