I've noticed that the trend is catching on and now there are a million different ways to implement them.
How do you use math notebooks in your class?
What are some great math notebooking ideas you love?

Kids start by writing the password of the day and then analyze three items to determine which one is good, which is better and which is best. Here's some examples...
Kids start by writing the password of the day and word of the day, both posted on the front board. Then they look up the word in a dictionary (this can be done with a partner if you don't have enough dictionaries) and write its definition, part of speech, a synonym and antonym for the word and the guide words at the top of the dictionary page. In the grid, they write a word that's an example of each corresponding part of speech. The last box is for them to use the word in a sentence and, if time, diagram the sentence. (In our class, we diagram sentences to help with grammar and writing structure; there's a great resource for learning to diagram sentences here)
This is a craze that has been going around Pinterest quite a bit lately! I tried it with my kids and they LOVED it, and it actually engaged my high kids and low kids the whole time. So I decided to add it to our morning starter book and have them do it every week, which will help develop phonics and word parts skills.
Each place value is color-coded so kids realize that each digit in a number has a different value. When they realize this, they no longer line up digits incorrectly because they understand that the ones have to be added to each other, the tens have to be added to each other, etc.
Expanded form is suddenly a piece of cake!
For older grades, there are also ones with decimals you can buy here.