[R] plotting a function with given formula in ggplot2

[Curiouslearn]

Hi All,

I have a scatter plot produced using ggplot2 and I want to add the
regression line to this scatter plot. I suppose I can use
geom_smooth() to do this, but for the sake of learning ( I am new both
to R and ggplot2), I want to try and add it as a function (something
that curve() does in the standard R plotting). I did some search and
found that stat_function() can be used for this. But somehow it is not
working. The following is my code. Can you please tell me where I am
going wrong and what the correct code would be:

reg1 <- lm(kid_score ~ mom_hs, data=iqdata)

scatter  <-  ggplot() + geom_point(data=iqdata,

aes(x=as.factor(mom_hs), y=kid_score) )
                               + xlab("Mother's High School Status")
                               + ylab("Children's Test Score")
                               + stat_function(fun=function(x)
coef(reg1)[1] + coef(reg1)[2] * x)

I understand that you probably do not have the data I am using (I am
trying this out from Gelman Hill's book on Multilevel models). But I
was hoping you may be able to point out the error without the data.

Thanks for your help.