Gather information on where the student has hit a plateau. For instance, a student might master multiplication but have trouble moving on to division. Determine the general area where the student is having trouble, but keep in mind that it isn't always going to be concrete.
Introduce the next level of knowledge, but keep it relative to skills the student has already mastered. For instance, if the student has plateaued at multiplication, introduce division as a process that is like multiplication, but the opposite. Placing new knowledge within the context of knowledge the student already has will help her visualize and achieve the next level of knowledge.
Engage the student in something he is interested in to lead him to the next level of knowledge. If a student loves to read, guide him forward with books or articles.
Create a series of small steps a student can follow. Instead of expecting a student to master the next skill, help her to see that she can take a series of steps to get there. This might require you to re-create pieces of your curriculum, which might be beneficial to other students as well.