An official ranking for DO schools doesn't exist because it is difficult to arrive at an agreement as to which DO schools are best. There are many factors that can influence the quality of a school. If I'm a primary care fanatic, then I might believe the DO school with the strongest rural medicine training is the best school. If I'm a research fanatic, then I might believe the DO school with the most research grant money is the best school. If I'm a specialty care fanatic, then I might believe the DO school with the greatest availability to academic tertiary care hospitals is the best school. If I'm an OMM fanatic, then I might believe the DO school with the most renouned OMM faculty is the best school. And the possiblities go on.