I would like to share with you one of my favorite tools for teaching math in K-2, Happy Numbers. This is fantastic website is a "teaching assistant" for math differentiation. Its curriculum is aligned with Common Core standards, and if you purchase an account for your class, you can assign specific tasks for individual or groups of students, and track their progress with detailed reports. Click below to visit their site and explore.
However, if you are only in the market for FREE resources, it's also wonderful!