I will admit that there is one type of worksheet that I used in the past and found relatively beneficial, although it had a different kind of flaw. For my Basic Math, Pre_Algebra, and Algebra classes, I had several books of "self_checking" worksheets. These worksheets had puns or puzzle questions at the top, and as the students worked the problems they were given some kind of code for choosing a letter to match that answer. If they worked the problems correctly, the letters eventually answered the pun or riddle. Students enjoyed these worksheets, but there are a couple problem areas even with these worksheets. Some students would get the answer to the riddle early and then work backward from letter to problem answer, so they weren't learning or practicing anything.
Have you ever noticed how many K┨ math content websites are devoted to math worksheets? There seems to be an increase in websites that cater to desperate teachers and parents by offering fast, free "worksheet generation", free fractions worksheets," etc. Now, as a former teacher I am not saying that one should never use math worksheets; however, I do believe that many teachers are using a very superficial method of instruction that relies too much on low_level math worksheets and hands_off instructional approaches. Worksheet lessons move from reading the directions aloud, to doing sample problems as a group, to completing the worksheet independently (or at home with parents), day in and day out. Teaching needs to be more than passing out worksheets. Whether you are the classroom teacher, instructional specialist, or parent, the methods you use greatly impact the level of understanding achieved by your students.