This is the creme de la creme of law schools. On the U.S. News chart, Tier I schools are those ranked between one and 50. Some of the usual suspects include Ivy League schools like Harvard and Stanford, as well as Public Ivies like UCLA. Tier I schools boast high undergraduate GPAs, low student-to-faculty ratios and high placement rates among graduates.
Tier II schools are ranked between 51 and 100. Theses schools still produce a stream of capable lawyers, but they don't have the prestige or the deep pockets of the Tier I schools. Since major law firms do occasionally hire from Tier II, you may want to attend one of them. However, understand that you will have to rank higher in your law school class upon graduation than an applicant from a Tier I school who is applying for the same job.
Tier three schools are not ranked; they are simply listed in alphabetical order. There are no dramatic differences among the Tier III schools, but collectively they all rank above each of the Tier IV schools. Tier III school do not have the same placement success and are not as well ranked by members of the legal academic community. However, some tier III schools have a good reputation in certain legal specialties like personal injury law.
Tier IV schools are at the bottom of the heap. Although it is possible to get a job after graduating from a Tier IV school (especially if you are applying to small firms), you should be at the top or very near the top of your class. If you are only accepted to Tier IV schools, you should check to see how they are ranked in specific legal specialties in which you are interested. If they are highly ranked in that specialty you might want to go Tier IV. If not, you might want to wait a year and go through the application process again.