Posters can be effective educational outreach tools, but only if they're done very well. Given their relatively high cost and potentially low impact, it's important to understand a few things about posters before producing them.
Independent evaluations indicate that educational material on the back of a poster drives teachers nuts. Even if the educational material is broken down very carefully and cleanly into standard-sized "pages," copying is very difficult. And once the poster has been hung up, the content on the back is gone and forgotten.
Remember that teachers and librarians have limited wall space. Bigger isn't always better.
Also, teachers respond differently to promotional versus educational posters. At a recent National Science Teachers Association conference, teachers were offered two series-related posters. Not a single teacher took the nicely illustrated promotional poster, but the other, which included a visual timeline of scientific events, ran out long before the conference was over.