Another site/link rec. from Dr. Nickie "Angles is a 4th Grade Standard in the CCSS. Here is a great set of activities to have students do in their math journals. I (Dr. Nickie) really like it because it is interactive, engaging and standards-based. Check it out!Types of Angles math journal @ Runde's Room."
Here's a terrific post with directions and resources on how to introduce fractions using paper folding! This is great for comparing and equivalence. It also helps cut down on all the cutting and gluing in the classroom!