[bolingbaker]

We could give you better advice if we knew to what sort of school your son was headed. Sorority rush is pretty much the same everywhere, but fraternity rush varies widely. Is he headed to a big state school in the mid-west (Missouri, Nebraska), a communter school (Memphis, Houston, UCF), a big southern campus (Georgia, FSU, Florida), or a northern school (MIT, Penn State, someplace in New England). Is it a small, private school? All this does make a difference.
The gentleman from Nebraska (Beta Theta Pi) told you about summer rush. Summer rush is big in a corridor from Arkansas west to Arizona, and north of that to Canada. Many if not most rushees actually pledge in the summer and move directly into the houses. In the rest of the country, summer can be a time to meet the rushees but there aren't many places where they actually take a pledge class in the summer prior to fall. Formal rush for men exists (Arkansas, Mississippi) but it is relatively rare.
The gentleman from Nebraska mentioned making a 'rush application', and he referred to 'bid cards'. Most public schools outside the midwest don't use such things and wouldn't know what they were if you asked about them. Rushees simply go meet the fraternities during rush, accept a bid and then go through a pledging ceremony at the end of rush.
One thing to keep in mind: there are some schools - Auburn and Alabama come to mind - where some fraternities restrict themselves rather severely to certain specific towns and even certain high schools. Don't be offended by that practice; it's just something they do.
Finally, with respect to the gentleman from Nebraska, I'd recommend that you steer your son toward the fraternities that are the traditional leaders (instead of, as he suggested, the place where he find the 'best fit'). In a given fraternity system there are groups that are strong and remain strong, and groups that wre weak and remain weak. A young man will not grow and prosper in a weak fraternity. In a strong chapter he will tend to rise to that standard, and be better for it. The fraternities that produce the powerful and influential leaders of tomorrow are not the weak ones.
Best of luck to your son.