Last week we celebrated our one hundredth day of school with several fun activities.  During math children engaged in several searches, which are always fun and motivating.   One was for 100 numbered tiles, which they matched  with their corresponding number on a hundreds chart.  The second was for tiny pictures of objects arranged in groups of 10 up to 100.  They used clipboards and recording charts to note the number of each kind of object once they found the picture (e.g. 20 hexagons or 90 little bears.)  Some children wrote numbers to 100 while others chose to make sets of 100 objects.  Throughout the day we worked on writing 100 words as a class.  Finally, with our third and fourth grade learning buddies, children created structures using 100 marshmallows and toothpicks.  While celebrating the 100th day is mostly about recognizing a milestone and having fun, I find that emphasis on 100 for a day or two can also deepen children's sense of our number system and how numbers to 100 are composed and written as groups of 10 and additional ones (42 is four tens and 2 ones, for example).