Boil the potatoes in a pot of lightly salted water just until you are able to stab one easily with a fork. Drain, then peel the potatoes when they are just cool enough to handle, and mash lightly.
In a separate pot, boil the string beans just until you can stab one with a fork. Drain, and chop the beans into 3 or 4 small pieces each. Add to the mashed potatoes and stir together.