So today, I did a google search for fraction worksheets and found several from HelpingWithMath.com and printed two that included mixed numbers and uncommon denominators.
Then, I had my students log onto Conceptua Math (I had already posted the link on their Edmodo site for easy access). They choose the free tool Adding with Uncommon Denominators.
Not only did my students work hard on their assignments, they also help each other! Once someone figured out how to manipulate their denominator they were excited to help their neighbors!
Only problem I had was they students all used my username that I created. I wish this website would allow for a teacher/student account options under the free version. The premium version offers much more, but our school cannot afford it.