My DD8 seeks them. We skipped her into 4th grade this year, and she works on the 4th grade workbook at times for amusement.
DW also picked up a trivia game with the same brand. DD has been handing me one of the card decks and asking to quiz each other most nights this week. She quit playing Minecraft with me early so we could do it last night.
I can't certify how the difficulty of the workbook rates for DD, but I can say there's a a good mix of easy and difficult (or at least, unknown) questions for her in the trivia deck.
