Well, I've never heard of it, either. Sounds a bit over the top to me!

Boy that's a new one for me too. Are they planning parties at school for the kids? I wonder if that's a regional thing- do you have an idea where those forum members are located?

I think it started in the 1990's. I remember being asked send in 100 of something with my daughters. Once I sent 100 pennies, another time 100 toothpicks.

I never heard of it before, but judging from the amount of dollar store junk being sold to "celebrate" it, it looks like just another Hallmark holiday created to sell stuff.

I feel certain it came about because math textbook series about 10 -15 years ago started doing what was called calendar math. It was a way of introducing concepts and revisiting them on a daily basis, usually done at the beginning of the day. One of the big things to do was to count the number of days in school. Everyday, a straw or something used that would visually count that day would be put in a cup (usually part of the calendar display). There would be 3 cups: one for the units or ones (1-9), another for the 10's (10-90) and a third for the hundreds.

For example on the 10th day of school, you would already have 9 straws in the units cup. On the 10th day you would add another but now you would band the 10 straws into one group of ten and move it to the tens cup. Ten means "1 ten and 0 units. As the year progresses, you would have say for the 75th day, 7groups in the 10's cup and 5 in the units. On the 100th day, you would already have 99 days in school; 9 groups of 10 in the 10s cup and 9 in the units cup. When you add the 1 straw for the 100th day, you would have 9 groups of 10 in the 10's cup and now 10 straws in the units cup. That means you move the 10 units into a group of 10. Now you have 10 groups in the 10s cup but that makes 100 straws so you band them and move it over to the 100's cup. So now there is one big group of 100, 0 ten's and 0 units. Schools would plan big celebrations about the 100th day of school, all centered around math, like measuring and comparing the length of 100 new crayons to 100 new pencils. Really it all was about math concepts and in this case PLACE VALUE. I loved calendar math in my kindergarten class. It really helped the children. One year I had an average student raise his hand on the 100th day of school when we were talking about what "100" means and he said "if there are 10 tens in 100 then there must be 100 tens in 1000. WOW!

Sorry this is probably way more than you wanted to know!

It's roughly "the half way mark"....It's mostly done in K-2...and it's used as a learning lesson at our elementaries..grouping, counting to 100, collections....

I think it must have started out as a math lesson but it seems almost world-wide now as the link below will show. I just don't know who/what to ask about it tried origin of howdid it start - begining of - and get sites that show what to do .
Thanks anyway.
This was one link I got as a response interesting

Here is a link that might be useful: TeachersFirst: 100th Day Ideas

My grandson is in kindergarten and they are learning to count to 100 and using increments of 100 - it's about teaching related to the number '100'. Darin is taking 100 new pennies.

I just emailed my DD, and this is her response.
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It started out as a way to count days with the lower grades. ThatÂs actually how we celebrate it at our schools. Each day we have a morning meeting and we count how many days weÂve been in school. So when we get to the 100th day, we might have some work sheets or art work that says, "IÂm 100 Days Smarter" or something like that. One year we all made "glasses" that we could wear that had a big 100 on them. We all looked like Elton John.

That's great if the '100 Days of School' can be translated into math projects and art projects. When I Googled I found plastic 100 Day glasses being sold along with key chains, baseball hats, t-shirts and other assorted junk. There is even about a dozen different children's story books being sold on Amazon with short stories about the 100 Days of School event.

There are sites with party ideas for the event and even the suggestion that the kid should be rewarded with a crisp new 100 dollar bill upon achieving this "milestone" in their lives.

Here is a link that might be useful: Junk

They started celebrating it here with their then new approach to primary math and teaching the importance of zero. Our school had a little character called Zero the Hero too.

It all had to do with teaching the importance of zero and the importance of the ones, tens, and hundreds columns and in counting in base 10.