Recently youngest dd and I did one of my favorite math lessons. It's a hands-on way to teach prime numbers.
Sure, you could teach prime and composite numbers simply by defining prime numbers as: "A Prime Number can be divided evenly only by 1 or itself. And it must be a whole number greater than 1."
[ http://www.mathsisfun.com/prime-composite-number.html ]
But what does that mean to a child??
Here are the steps I use to teach prime numbers:
1. The child uses some kind of marker (I strongly prefer translucent chips because you can see the numbers underneath - I believe mine are from Learning Resources) to physically cover up the multiples of numbers on a hundred board. They start with the 2s and cover up all of the multiples of 2s (NOT including 2 or the number of the times table that they are doing). Then they do the same for the 3s, leaving the previously placed chips. And so on until they do the 10s. Dd said, "We don't have to do the tens because they are already covered," since she can swiftly see that they are already covered by then. At this point I give the name and definition of prime/composite numbers. Sorry the photo is fuzzy but it gives you the idea.
You can find a hundred board like THIS
for about $1-ish at teacher supply stores or Mardel. Or there are many other styles that are more durable like THESE.
2. To self-correct I gave dd a list of prime numbers that I had printed off the net. She went through and checked her chip placement to make sure all the primes were NOT covered. Then she went back through again to make sure all of her blank ones were prime numbers. So, she checked all those covered with chips and uncovered (I noticed that only checking it one way was leaving a few composite numbers uncovered so I suggested the other check as well). She self-corrected without me.
Here are a few links that list the prime numbers only. I don't see any like the one I had in my folder (in 2 columns and very easy to read) but I hope these will help. I used a list that ONLY had primes on it so as not to make it too cluttered for a control.
http://www.mathcaptain.com/number-sense/prime-numbers.html (scroll down for the list)
3. Using her hundreds board as the self-correcting material this time, she circled all of the prime numbers on a printed hundreds chart in the color of her choice (all the same color). She then chose a different color and lightly colored over the composite numbers. She was using map pencils for this part.
4. She then cut out the hundreds chart and put in in her Math Notebook with a heading of Prime Numbers We use quadrille, or graph paper, notebooks. HERE are some if you can't find them locally. Underneath that she listed the prime numbers in column form. And then... she took a break from school and puppy responsibilities to play with Polly Pockets in the doll house :).
Nothing with excitiotoxins, if I can help it! Here is an old, but excellent, book:
Excitotoxins: The Taste That Kills
I read it years ago in the middle of bad neurolyme so I don't remember details to explain it. However, I remember it was clear, well-written, and easy to understand. My library had it - maybe yours does too :). This is one of the main reasons that I avoid giving my children any MSG (which is cleverly hidden by processed food makers in their labels). The other reason is that I get MSG-headaches. The other day I hadn't even left the restaurant yet before it hit me!