Pre-post using historical data and experimental group

I want to see if there is statistical significance of improved posttest scores (DV) using IV (formative assessment) with my intervention group. We have never implemented before and give pretests and posttests for each of our classes. Historical data of 1100 former students show an average .61 and post .81. I'd like to see if the IV improves posttest scores. Since I'm using past data of student average scores and an intervention group, what design /method should I use? Thank you