One of the big stumbling blocks in maths is working with fractions, especially addition, subtraction, multiplication and division. The problem is caused by a lack of understanding of what a fraction actually means and how they can be manipulated to make the task easier. (Equivalent fractions being the key.)
A common fault when adding fractions is for a child to simply add the two top numbers and then add the two bottom numbers. This will always lead to a wrong answer and it is important to stress to children that to add two fractions the bottom numbers (denominators) must be the same. The reason for this can easily be shown by cutting a shape in to different sized parts and then asking how much two of the parts could be.
This particular worksheet takes all the stress out of the problem as the denominators are already the same for each addition question. Where an answer can be simplified a further answer is expected.