That was the problem I had. The squash and beans took over. The corn never had a bit of a chance. I think that when the native Americans did it, they grew a bean that was not as vigorous in it's runner growth, their corn was a taller flint or dent corn, and the entire crop was designed to be harvested all at once at the end of the growing season. Not like us folks who want succulent sweet corn, tender green beans, and the squash crop as well.
One thing that you could try, that might make the concept work, is to grow bush beans, with a hill or row of corn in between the rows of beans, and then plant your squash where ever it makes the most sense, but provide a rigid trellis for it to climb so it doesn't tear down the corn. There are also beans that are described as "half runner". As the name implies, they don't grow as long as a pole bean, but taller than a bush bean.
