mind your p's and q's

Pay attention to details: “We want this operation to run smoothly, so everyone please mind your p's and q's.” When learning to write, children often reverse these letters, so the teacher would admonish the students to be extra careful when writing them.

The New Dictionary of Cultural Literacy, Third Edition Copyright © 2005 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.