Here are 3 strategies for students to use when dealing with measurement.
The first strategy has them taking the unit (5 feet and 4 inches for example) and then creating a fraction based on the larger unit. (In this case, it would become 5 and 4/12 feet.) Once changed into a fraction, they can use their ability to add and subtract fractions, and then they would change their final answer into a mixed unit of feet and inches.
Strategy #1: Fraction Strategy
The second strategy involves regrouping. This strategy is confusing to some students because when we regroup, we normally regroup with units of base ten, but measurements do not always conform to this so it is important they understand they must regroup using the number in the given unit.
Strategy #2: Regrouping Strategy
The third strategy involves changing the mixed unit into one unit, the smallest unit. So something like 3 feet 7 inches becomes 36 inches plus 7 inches, or 43 inches.
Strategy #3: All One Unit
Depending on your student's ability, you might have to spend some time on the basic prerequisite skills. So for the first one, you might need to spend some time converting feet and inches to feet with a fractional part. For the second, you might need to spend some time regrouping with units that are not base 10. For the third, you might need to spend some time converting into the smallest unit, so 3 yards and 2 feet is equal to 9 feet plus 2 feet, or 11 feet.