You can find worksheets for a wide range of courses--almost any course you want to teach your children. These include spelling, writing, English, history, math, music, geography, and others.
Or you can usually find textbooks and workbooks at the public library, where you can also copy any worksheets that you want to use.
It is amazing the difference in effort you will get from worksheet to worksheet. Granted the amount of effort may vary immensely from year to year depending on the group of students you have.
Once you have a scope and sequence book, make a list of each area in math that he needs to work on for the school year. For example for grades three and four, by the end of the year in subtraction, your child should be able to: