We don’t want our children to be part of a captive national audience for a self-serving political speech — by President Obama or any politician.

I’m glad to see at least one school principal has the sense to let parents shield their kids from that kind of propaganda, but parents shouldn’t have to opt their children out of an event where, until hours ago, they were going to be asked to “write letters to themselves about what they can do to help the president.”

Lest you think this is an isolated lapse of good judgment, read Michelle Malkin’s latest column, which documents “the activist tradition of government schools” in great detail. Here’s a taste of it:

Zealous teachers’ unions have enlisted captive schoolchildren as letter-writers in their campaigns for higher education spending. Out-of-control activists have enlisted their secondary-school charges in pro-illegal immigration protests, gay marriage ceremonies, environmental propaganda stunts, and anti-war events.

And last year’s presidential campaign saw disgraceful abuses of power by pro-Obama instructors. In New Rochelle, New York, elementary students were given an in-class assignment to color in drawings of Barack Obama — including a picture of a campaign button featuring his face and the slogan “Students for Obama 2008.”

In Cumberland County, N.C., a fifth-grade-school teacher turned a “civics” discussion into an unhinged harangue against a girl who said her family supported John McCain.

That’s why “Mommy” is also “Mrs. Glover” to the three impressionable children in our home.

(Read previous “Why We Home-School” lessons.)