Each fraction has a common factor in the numerator and denominator, and the student divides both by it to write the fraction in lowest terms. There are no already-reduced fractions on the sheet - every one has work to do.
This is the skill behind every fraction answer key on the site, which writes results in lowest terms. Practising it on its own makes the arithmetic pages easier to check.
Find the largest number that divides both the numerator and the denominator, and divide both by it. 6/8 has a common factor of 2, so it becomes 3/4.
No. Every fraction on this page has a common factor greater than 1, so there is always something to cancel.
Fourth grade introduces it; fifth grade expects it to be automatic, because every fraction answer is written in lowest terms from then on.
Yes - turn on Include Answer Pages and the reduced form of every fraction prints on a matching key.