Many students have trouble with division; mostly due to not understanding the concept. Partially, due to not knowing multiplication fully. Many may have been absent from school on the critical day it was explained.
Division is just counting how many times you can subtract on number (divisor) from another number (dividend). The number of times you can subtract is called the quotient and any number smaller the divisor remaining is called the remainder.
Click the Start box to see lesson; click Sub as Add to see work with negative numbers

While many can understand the subtraction method, the teacher jumps quickly to a short cut. This short cut is based on know you multiplication tables well!
Most teachers feel knowing the time tables though 12 is sufficient; personally, I found knowing them through the 16s lit the concept into my skill set.