Many students have a hard time grasping numbers on pages. Those who need extra help often benefit from graphics and visual representations, sometimes long after other students have moved on to working with the more abstract numerical problems. Simply giving students problems in graphic form is often not enough, however; you must then work with students to ensure they engage with the graphics and understand what the problem is asking. Using objects students can actually hold and touch, such as paper clips or buttons, can help the math become more concrete. Show them how to translate simple problems on their own from abstract, such as 4 - 2, into concrete terms, such as tally marks or objects.
Many students have trouble remembering facts, a necessary skill on which much of higher math is predicated. To help them remember facts, separate arithmetic problems into separate sets -- for example, subtraction only -- until students become fluent with those types of problems. Provide concrete tools, such as number lines or manipulatives, for students to work with. Avoid competitive activities that stress students and do not improve memory. In severe situations, only add a single fact at a time, and work on that fact until the student has mastered it.
Confusing vocabulary is a main problem in students who have trouble understanding math, especially since math and reading disabilities often go hand in hand. Before beginning a unit, teach the necessary vocabulary using both pictorial and concrete or physical representations. Check students on their understanding of vocabulary before proceeding with every lesson, and use mnemonic devices to help them remember terms. Always be consistent with terms, for instance using "subtract" every time you talk about subtraction, and reminding students who use "minus" that this actually means "subtract."
Helping students correct their own errors is another method of aiding them. Perform multiple problem sets with students, use worksheets and quizzes, talk to them and ask them to model thinking through a problem out loud to see where the errors in their thinking are. Then draw up a checklist that addresses those errors. For example, a line on a list about fractions might be "Did I put the numerator and the denominator in the right place?" Model using the checklist before giving it to students to use on their own, then praise them when they successfully use it.