\begin{Schunk}
\begin{Sinput}
 m1mf <- model.frame(m1)
 m1mf[ , "education"] <- m1mf[, "education"] - mean(m1mf[ , "education"], na.rm = TRUE) 
 m3 <- lm( prestige ~ education * type, data=m1mf)
 summary(m3)
\end{Sinput}
\end{Schunk}
