library(lme4)

data <- c(
 287,283,261,298,302,280,
 211,272,222,285,253,252,
 266,252,287,266,255,269,
 299,310,285,296,310,301,
 288,265,273,285,252,259,
 295,299,285,288,281,303)

rt.df <- data.frame(rt=data,
 rep = factor(rep(paste("rep",1:3, sep=""),12)),
 prepost = factor(rep(c(rep("pre",3),rep("post",3)),6)),
 subj = factor(rep(paste("subj",1:6,sep=""),c(6,6,6,6,6,6))),
 Group = factor(c(rep("Treat",18),rep("Control",18))))

fm1 <- lmer(rt ~ Group*prepost + (1|subj), rt.df)
fm1