There are many types of manipulatives used to teach fractions. Fraction circles, fraction bars, and measuring cups are my favorite. The circles are divided into different fractions, often with color-coding to distinguish among the fractions visually. Fraction bars or fraction tiles are similar to fraction circles but have rectangular shapes. Measuring cups are also an excellent tool to use. They can physically pour water ( 1/4 c) into 1 cup. They will see that if you add four- 1/4th cups, you will get a whole cup. Legos work well because of the multiple sizes that work down to one-eighth. Cuisenaire rods and pattern blocks can also be used to model fractions. I found these awesome videos from the National Intervention Center. Intensive Intervention link.