I teach my 6th graders to "Please Excuse My Dear Aunt Sally" to remember the order of mathematical operations: parenthesis, exponents, multiply, divide, add, subtract.
Jean, MI

I teach my third graders to think of the sentence, "My Very Educated Mother Just Sent Us Nine Pizzas" to help remember the names of the planets in order from the Sun outward. (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto)
Kathy Bowen, Bakersfield, CA

Many students have difficulty when converting measurements. For example, if the assignment asks students to convert feet to inches or pints to cups they are confused as to whether they should multiply or divide to find the answer.

Several years ago my third graders helped me come up with these sentences to help us remember. The students know that if they are changing something from a SMALLER unit to a LARGER unit, they will DIVIDE, because Snails Love Dessert. Conversely, they understand that if they are changing a LARGER unit to a SMALLER unit, they will MULTIPLY, because Llamas Slurp Milk.

Deanne Townsend, Woodstock, GA

To help our fourth graders remember the steps for long division, we use the following phrase: "Does McDonald's Sell Cheeseburgers Raw?"

The steps are as follows: divide, multiply, subtract, compare, remainder. In the margin, they write the first letter of each word in the phrase in order and check off each letter as they do that step. They never forget how to do long division this way!!!

Wanda, Houston, TX

To remember the directions on a compass, my students say "Never eat soggy worms".
Emmy, Ardmore, OK

To spell "separate" correctly, think that separate has "a rat" in it. Here's an old one: geography– George Edwards Old Grandmother Rode A Pig Home Yesterday .
Linda Wing, Buffalo, NY

I tell my students to say "nice dog" to help them remember that the numerator is over the denominator. I have a few more:

N.E.W.S. to remember cardinal directions
SEAN got three AAA's to remember the continents: S = South America; E = Europe A = Asia; N = North America; A = Africa; A = Antartica; A = Australia.

Sandra Bembry, Centerville, GA

This is one I learned in Junior High to remember the colors of the rainbow. "Roy G.Biv" (red, orange, yellow, green, blue, indigo, violet). I always check myself by it.
Andrea, Orlando, FL

In third grade, teaching subtraction which requires trading, regrouping, and borrowing can be difficult. I use a phrase I learned many years ago: " Bigger bottom, better borrow." It has helped my students.
M. Quinn, Monroe, CT

RIDER is a mnemonic device that helps children to form visual images as they read narrative text. Many children are taught to read with a code-based, "figure out the word and you've read" method and come to second or third grade able to read the words but having no idea what those words mean. RIDER helps them to see that reading is getting meaning from those words.

Get a high-imagery selection of text at the child's instructional level. (If the material is too difficult for a child to read at least 90-95% accurately, choose something else.) Cover any pictures to make sure the child is using the words to make an image (not the illustrator's image to make an image).

R – Read the first sentence.
I – Make a picture in your mind.
D – Describe the picture you see.
E – Evaluate if your picture makes sense with the story thus far.