I picked these books up for my six year old, who is reading slightly more advanced books than for hs age. He found them exciting to read aloud to us, and the short chapters meant we could read a little at a time without finding it too much of a slog. We chose to read alternate pages to each other in the longer chapters. The story was fast paced, with good cliffhangers at the end of each chapter making it exciting and leaving my son wanting to read more. The content wasn't too scary, and I think it would appeal to 6-9 yr olds quite well. You can't beat a good spy story for boys!!