It really is an apples and oranges compare, I'd say to find students from that lower socioeconomic strata that can make it through the curriculum and want to attend an Honor Code bound school is downright impossible for BYU recruiting and admissions.

It feels like there are two classifications of social mobility per this quote, 'Calculating BYU’s success rate among males only, or using total household income, places BYU among the nation’s top 10 and 15 percent, respectively.'

Who is Brookings to say that isn't social mobility, are BYU grads moving from the lower middle class to the upper middle class? They don't even attempt to answer that question, instead just focusing on the poverty population that isn't as common amongst BYU's applicant pool.