Our nation's greatest asset. North Shore Country Day School on flickr The largest asset on Uncle Sam's balance sheet is not U.S. Official Reserve Assets, nor Total Mortgages, nor Taxes Receivable.

The correct answer, as of the latest Flow of Funds report for Q1 2012, is ... Student Loans.

The rapid growth in student debt has been a frequent topic in the financial press.

One stunning chart that caught my attention illustrated the rapid growth in federal loans to students since the onset of the great recession.

Here is a chart based on data from the Flow of Funds Table L.105, which shows the Federal Government's assets and liabilities.

As I point out on the chart, the two callouts are for Q4 2007, the quarter in which the Great Recession began (December 2007) the most recent quarter on record, Q1 2012. The loan balance has risen and astonishing 332% over that timeframe, most of which dates from after the recession.

This chart only includes federal loans to students. Private loans make up an even larger amount. Earlier this year the Consumer Financial Protection Bureau (CFPB) posted an article with the attention-grabbing title: Too Big to Fail: Student debt hits a trillion. The details of the private student loan market are not readily available, but CFPB plans to publish its study results on the topic this summer.

But back to our quiz. Student loans may be a liability on the consumer balance sheet, but they constitute an asset for Uncle Sam. Just how big? Nearly 35% of the total federal assets, over four times the 8.6% percent for the total mortgages outstanding.

Of course, assets are, sadly, the trivial side of Uncle Sam's Flow of Funds balance sheet -- about 1.36 Trillion. The liability side totaled 12.65 Trillion at the end of Q1 (details here).

Student loan debt is something we'll want to continue watching, especially when more details of the private loan market becomes available.

Footnote: For those who wonder how much the pie chart above differs from the Q4 2011 version, here's the previous version, based on the data reported in the March 8, 2012 release.