During the winter of 2011, the author faced an instructional dilemma: Should she teach the concept of adding and subtracting fractions with unlike denominators using a "quick trick" for the sake of staying on schedule, or should she try something different in hopes that her students would gain understanding through their own methods? The latter seemed the better option, but she knew it would take time and involve selecting strategic problems to cultivate such understanding. She was up for the undertaking, knowing that this teaching risk would benefit all her students if she designed problems that differentiated for their learning needs. Because she taught a fourth- and fifth-grade combination, she had to develop lessons that were accessible for students in both grades. Creating problems that were based on Cognitively Guided Instruction (CGI) (Carpenter et al. 1999), she used differentiated number sets within the problem structures. By spending three days with these rich problems, her students gained their own understanding of the topic, and thereby, they did not lose time later in the year remediating for adding and subtracting of unlike denominators. (Contains 4 figures.)