A lot of the websites charge high dollar amount for these math worksheets. Considering your willingness to spend the high dollar, you run in to a new problem _ the uniqueness of the material, a lot of websites offer sheets packed with identical problems leading the child to almost rote memorization of the problems and solution. This leads to deprivation of student and his/her ability to solve the problems logically. And some websites offer sheets in portable document format. And to open such sheets you are forced to download special software.
Another problem with almost all worksheets is that they don't prevent incorrect answers. Self_checking worksheets just let the student know they did something wrong__after the fact. I am a firm believer in the concept that, if at all possible, learning should be structured in small chunks in such a way that there is very little possibility for error. Worksheets often allow for mistakes to be made and then to be repeated many times. A mistake that gets practiced is extremely difficult to correct. This especially happens when worksheets are used as time fillers or baby sitters and the work isn't really being supervised.