I've always taught that when saying a number, "and" is reserved for the decimal point. A LOT of my students this year say "and" in the number. Example: One hundred and thirty-six. Is it wrong to correct them so they only use it with decimals? Some of my students just can't seem to stop saying it. Any thoughts on this?

Our math text explicitly says to stop them from using the word "and" in this way as it is used to denote a decimal number. So, to avoid confusion later, stop them now.

I have a bad habit of saying it. I did not realize it until a 4th grade teacher asked us to make sure the 3rd graders were not doing it. Last year, I made a habit to correct the 1st and 2nd graders from saying it. Maybe try talking about money.

My prinicipal always says "two thousand AND ten" during morning announcements. We giggle because I make such a deal out of "and" meaning there is a decimal point in the number.

Correct them. I teach the correct way in K. I actually remember the moment I learned that rule in 5th grade. Up until that point, I'd had no idea.

It mostly comes up in my class when saying the year and then after the 100th day of school when we're counting over 100. I do tell them that many adults don't know the rule, so they may hear it incorrectly a lot.

my students immediately. I also show them on the board what the number looks like when they say "and". If they are telling my what to write I write it exactly as they say it. It helps for them to see the difference.

correct it, but like other PP have stated they hear it everywhere. I remember one year during a presidential election, I had my students count the number of times a news journalist used "and" in the middle of a number. We made a graph of the numbers the next day in math class. It was a fun experiment, and a great time to point out - just because everyone is jumping off the building doesn't mean you have to follow them! It is hard to stop when they hear it everywhere.