Margi, I saw your post, too.
Our district took three tries in 8 years before we passed a referendum to get our new $42 mil high school built. It passed by a very narrow 52% margin and has divided our city because of it. Over 1/2 of our city is retired and our state is one of the top five in the nation with highest property taxes.
For a pricetag of your size, a referendum may be needed and taxpayer money to pay.
I think what helped to pass our referendum, was the district created a committee from all aspects and age groups of the community.
Example: a pastor from a local church, another from the senior center, a retired teacher, business man, blue collar, parents of young children, middle school and high schoolers, alumni - even current seniors that were graduating.
This committee was formed 1 year before the voting date and they strategically planned what exactly our district needed, the best location to build, how much it would end up costing the taxpayers. (now actually is a good time to build since the interest rates are so low).
The committee also had public forums during the process (we called it the "referendum road show") and went to EVERY school function with maps, architectural drawings and fact sheets. They went to elementary school sock hops, spring flings, basketball games, PTO meetings and spoke to parents on every level of the school district on how this school was needed.
Then the hard work began... literally door to door (eyeball to eyeball) -- the footwork has to be done. Signs and flyers end up in the trash. You have to knock on doors - talk to people about why this new school should be built. Don't bother trying to sway the vote of the people against the project. They already have their mind made up.
Target the sleep-deprived parents in your community with little children. They are clueless. They are busy with diapers, trying to make ends meet and the day to day deliriousness that new parents deal with. THOSE are the people you need to get out and vote.
Good luck, but it will be a lot of hard work and a LOT of meetings and discussion. I lost an entire month before the voting date with meetings and discussions almost every night.
In the end, if it passes, the satisfaction is awesome. If it doesn't pass, keep trying.
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