R help - Nov 2009 - Stat question mixed models with time varying covariate

Please xcuse me for being slightly off-topic and cross-posting

I have a data set of schools, with scores for 4 years.  The goal is to evaluate
the effect of an intervention on the scores, accounting for some covariates
which are not problematic.  The chief problem is that the intervention could
take place in any or all of the 4 years.

I've thought of doing separate analysis for each pair of years, but this has
all the problems associated with pre- post- designs, and results in multiple
models to interpret.

Is there a way to use mixed models here?

I've tried googling but found little

TIA

Peter

Peter L. Flom, PhD
Statistical Consultant
Website: www DOT peterflomconsulting DOT com
Writing; http://www.associatedcontent.com/user/582880/peter_flom.html
Twitter:   @peterflom