This report describes several properties of Wainer and Wright's (1980) jackknifed ability estimator. These properties are as follows: the first order asymptotic behavior of the standard jackknife, including consistency properties; the first order asymptotic behavior of the general M-type robustified jackknife including consistency properties and formulas for the standard error; and a small sample distribution-free formula for the standard error of the standard jackknife. (21pp.)