A-Level Geography student over here.
Constructive margin = divergent plate boundary
Volcanoes at divergent plate boundaries tend to be shield volcanoes which are made of layers of lava. It is of a lower magnitude because it is a much shallower volcano than a composite volcano as well as the lava running out of it is very runny and fast flowing (it's basaltic if you're an a-level student) and they happen more frequently and because they happen more frequently, the lava doesn't form a crater (which turns into volcanic bombs)
Give an example if you're in doubt! I believe there is a shield volcano in Iceland so always have an example on the ready!
Hope this helps!
More frequent quiet eruptions