... so i have to teach standard deviation and variance tomorrow

[Chewbacca]

Ask the students to create (i.e. fake) a series of coin flip of a fair coin. Tell the to record each flip as either H or T. Depending on how much time you have do 10 or 20.

Then ask them to take out a coin and do the real thing again recording the results.

Now make stem and leaf plots of "total number of heads" and "max heads or tails in a row" with the fake data on one side and the real data on the other side of the stem.

For example TTTHTTHHHH has 5 heads and a max string length of 4 heads (only 3 tails in a row).

While this is actually also a great way to teach about location parameters and the general concept and misunderstanding of randomness, you can teach variance from this just as easily.

Also, in my personal opinion std dev is just a matter of units. Variance is the spice of life and std dev is an afterthought. That is because variance is in squared units.