Horses grazed on rolling hills in the background last year as Gov. Martin O'Malley officially announced his administration would pursue slot-machine legislation.

If that event were held now, the backdrop likely would be a crumbling school flanked by trailers, showing outdated books and overcrowded classrooms.

As the pro-slots side shapes its message for the November referendum on slots, the benefits the money could have for horse racing have largely been pushed to the background in favor of a focus on the impact it could have on education funding.

When Mr. O'Malley first outlined his slots plan, which eventually became a...