The concept of mean (average) for 5th grade math (also mode)
What does the mean (average) of a data set actually signify? This lesson doesn't focus on HOW to calculate it (though I cover that too), but instead, presents several example problems that involve the arithmetic mean in some manner.
In the last problem I ask, can you calculate the average from the info given in a bar graph (about people's favorite berries)? This then leads us to use MODE, another statistical measure of center.
See also
Introduction to primes — video lesson
Math Mammoth Grade 5 curriculum