I have never been in a classroom higher than first grade, so I have never seen subtraction, multiplication, or division taught or practiced in a classroom.
This past week I saw an excellent lesson about measurement. My teacher asked the students to bring in a "pet rock." She allowed the students to decorate their rocks as a special activity with me and as we decorated them I asked them to compare their rocks: which one was bigger, which one was heavier, which one was smoother, etc. Although this was impromptu and informal, the activity introduced the concept of weight and making comparisons between objects.
Mrs. Gajda has also done morning work with measurement concepts. On Halloween, the students used candy corn as an informal unit of measurement to measure line lengths and were then able to eat their candy. This was the first time I had seen a measurement lesson; they have not yet covered estimation or standard units of measurement. The candy corn lesson was a good introduction to units of measurement, as well as the concepts of longer/shorter.
Mrs. Gajda has not talked about area, but she does have tangrams in her classroom for early finishers so I suppose that can be seen as an informal introduction to area. Later this year she will use the tangrams to figure out which combination of shapes match up with others (i.e. have the same area.) Volume and capacity are also concepts above the first grade level that I have not seen taught, directly or indirectly.
The students in my classroom cannot tell time yet, but Mrs. Gajda is using calendar math to introduce time. For each school day, the students color in another minute on an analog clock. When they reach sixty days, she will talk about how the spaces on the clock represent minutes and that one fully colored clock is 60 notches/60 minutes, or one hour.