Which one is “most common” mean ,median, or mode. and why?

Mode. This one stands for the most common. This is the one that shows up the most out of a sequence of numbers.
Median is "median" or "middle" number.
Mean is the average of all of the numbers. 

Your answer is mode.

So my 5th grade teacher taugh us these with a song she called central tendencies by the beat of lazy song by bruno mars.

Finding MEAN is known as the AVERAGE, just add up all the numbers you have, then divide by how many you add, it's just two steps which isn't bad that's how you find the MEAN or AVERAGE

Now to find the MEDIAN which is in the middle line the numers up but just keep it simple in order from the least to greatest, but if there's two in the middle add and then divide find the mean of both set the median aside

To find the MODE it repeats the most     

Oh yes the Range the Range subtract the high and low