If future high school classes ever study the recent conflict over the AP U.S. history curriculum in Jefferson County, Colo., they will probably learn it was a battle in America’s endless culture wars.

At least that’s what they’ll learn if the history books reflect the predominant media narrative about the uproar: Concerned students, parents and teachers rose up against what they saw as right-wing thought control by the Denver suburb’s conservative-led school board, which had floated a plan to ensure that AP US history “promote[s] citizenship, patriotism, essentials and benefits of the free enterprise system” and does “not encourage or condone civil disorder [or] social strife.”

Having spent several days reviewing events in conversations with people on both sides in “JeffCo,” however, I have a slightly different take. The real moral of the story is that conservative school reformers have some good ideas, but they need to be a lot smarter about carrying them out than the Jefferson County Board of Education was – because their opponents, including teachers unions, will pounce on their slightest mistake.

To understand what happened in Jefferson County, you have to understand what happened next door in Douglas County, a heavily Republican suburb, over the last few years. “DougCo” voters elected conservative reformers to the school board who implemented a strong school-choice policy agenda. When the contract with the teachers union expired, the board ended both collective bargaining and the union dues check-off on teacher paychecks. These actions were perfectly legal in Colorado and the union was helpless to reverse them.

Then, in 2013, three conservatives won the election for Jefferson County’s five-member school board, backed by the same forces – the Colorado chapter of Americans for Prosperity (of Koch brothers fame) and school-choice activists such as Steve Schuck, a Colorado Springs real estate developer – that had supported the Douglas County conservatives.

Suddenly, the union feared a repeat of the “DougCo” ouster – only this time in 86,000-student JeffCo, the state’s second largest school district, where affiliates of the National Education Association collect millions of dollars in dues each year...