This is a Freebie I am putting out here to help kiddos who are having a hard time counting from 100-500. I've eased them into it by having them skip count by 2's on the evens, then the odds to help them recognize patterns in the grid, as well as get them accustomed to how we write past 100 - hundreds place, tens place and ones place. It gives them great practice saying the numbers as well. Then they move on to writing in groups of 10 going straight across the rows to again get them use to seeing patterns in the grid. Then the last grid is random chunks of 10. Each sheet is meant to take about 20 minutes if working with students who need remediation.
Look for the dry-erase 100's chart that allows your students to customize which hundred they're working with to help them with this activity, and any other counting past 100 activity.
If your students are still struggling, look for more Counting to 500 worksheets, or remediation tools.