Imagine that you had the money to send your child to any private college in the country. Then imagine that your kid was talented enough to be accepted at any college in the country. With all those choices, you'd still want a college that delivered the best bang for the buck, wouldn't you? In the real world, where money is tight and your selection limited, you have every reason to expect the same thing.We're here to help. As always, our 2011-12 rankings of the best values in private colleges and universities identify institutions that are both academically strong and affordable -- our definition of value. This year, however, we took a fresh look at the criteria that go into that definition to better reflect the matters that affect real families, and we tweaked our presentation so you can better fit the school to your circumstances.Saving for collegeFor example, we now assign more points to the four-year graduation rate than to the five-year rate -- the faster your student graduates, the more money you save. Freshman retention -- the percentage of students who return after the first year -- remains a major factor in our rankings. "It tells you whether this is likely to be a good school for the long haul," says Jane Wellman of the Delta Project, which studies college finance. On the cost side, we give added weight to colleges that rein in student debt.Those changes have sharpened our focus, but they don't turn the previous rankings on their head. Princeton, this year's No. 1 value among private universities, has appeared at or near the top of our list for several years running, thanks to its outstanding academic quality and generous financial aid policies. Pomona, ranked first among liberal arts colleges, makes its third appearance at the top of the liberal arts list for a similarly stellar showing. In each case, the new criteria confirmed what we already knew Rosetta Stone Chinese : These schools deliver consistently great value.Higher costs, more aidIn this struggling economy, you'd think that private schools would have priced themselves out of the market. In fact, enrollment at these schools is rising, and not just among the affluent. Private colleges are attracting more low-income students, students who are the first in their family to attend college and students of color, says David Warren of the National Association of Independent Colleges and Universities. Meanwhile, sticker prices keep rising, by an average annual rate of about 4.5%. The price tag at private institutions currently runs an average of about $37,000 a year; many colleges blew past the $50,000 mark several years ago.Still, "the important thing is to not obsess on posted tuition, because there is so much financial aid out there," says Ronald Ehrenberg, the director of the Cornell Higher Education Research Institute. That aid allows more students -- including low-income ones -- to attend. The need-based aid packages in our list generally rose in lockstep with rising prices. At Princeton, average aid knocks the total cost from $50,269 a year to less than $16,000, a bargain by any definition. At Pomona, aid reduces the $54,010 sticker price to less than $20,000.Most top-tier schools, including Princeton and Pomona, restrict their financial aid to families with need; lower-tier colleges woo students with merit scholarships (otherwise known as tuition discounts). Those discounts reduce the price for freshmen by an average of 49%, according to the National Association of College and University Business Officers.