Block scheduling means teachers must change their lesson plans and teaching techniques. Redrawing attendance center boundaries means parents and students must adjust to a new school. Adding a few minutes to the school day may require parents to rearrange carpools and childcare. And people don't like to be changed when the change is required of them by others. Your efforts to involve people and build awareness and support should begin when the problem emerges, not when you have a solution in mind.
People are more likely to support a solution when they have been part of developing it.
Your strongest allies should be close at hand. No matter what change you are considering, work hard and early to build understanding and support among the school staff. Teachers, administrators and support staff are in the best position to foresee the practical implications of implementing a change. Use their input as the change takes shape. 10-20 percent are opponents, who will remain loudly and permanently in opposition.