To correct for the effects of measurement error on structural parameter estimates, many researchers are now estimating models of educational achievement with LISREL. In order to estimate such models it is desirable to obtain multiple manifest measures of the latent constructs. Many researchers restrict their models to two manifest measures per latent construct for reasons of economy, but doing so assumes, in the absence of external information, that all of the covariance between the within-variable measures is reliable covariance. Such an assumption may or may not hold in practice. The present study empirically investigated the extent of within-variable, between-occasion error covariances among nine socioeconomic variables typically included in models of educational achievement using data on 1064 white respondents from High School and Beyond. Little evidence was found to support the claim that reliability estimates for social background variables are inflated due to correlated errors of measurement. (Author/BS)