The S&P’s Case-Shiller National Home Price Index dropped by a record 15.4 percent during the second quarter from the same period a year ago.

The index released Tuesday showed home prices falling by the sharpest rate ever in the second quarter considered to be a buying season.

The monthly indices also registered record declines. The 20-city index dropped by 15.9 percent in June compared with the same month last year. This largest drop since the index was started in 2000. The 10-city index fell 17 percent, its biggest decline in its 21-year history.

However, the rate of single-family home price declines slowed from May to June, suggesting that the gravity of the housing slump may be waning.

“While there is no national turnaround in residential real estate prices, it is possible that we are seeing some regions struggling to come back, which has resulted in some moderation in price declines at the national level” said David M. Blitzer, chairman of the index committee at S&P.

Also, fourteen cities in the monthly index showed improvements from May to June and nine recorded positive returns.

Still, on a year-over-year basis, no city in the Case-Shiller 20-city index saw price gains in June, the third straight month that’s happened.

Las Vegas topped the list of decliners, plunging 28.6 percent followed by Miami at 28.3 percent and Phoenix with 27.9 percent.

Charlotte, N.C., the last city in the index to report depreciation during the current housing downturn, posted its largest drop since 1991 at 1 percent.