I think this is a really important book that kids should be exposed to. Is it perfect? Absolutely not! But the great things about it outweigh the less great things.
Ever since Dennis' mother left them, he's missed out on a lot of things. His father turns to comfort eating (well described in the book, although there is also an element of fat-shaming that I find Walliams uses too often) and isn't at all affectionate. He's obsessed with a photo of a yellow dress his mother used to wear, and then sees one just like it on the cover of Vogue. He sneakily buys a copy, and becomes entranced by the beautiful images among the pages. He ends up meeting Lisa, who is always dressed impeccably. It is Lisa that ends up giving him a dress of his own he can wear.
Rating: 4.5 out of 5. I do have a couple of issues with it, but overall it was great.
Age Range: 9 or 10+. Maybe. There's a couple of references that will hopefully go over kids heads (see content notes) or maybe not!
Ability Range: 8+ for confident readers. Walliams writing is easy to get through and the only tricky vocabulary would really be for non-Brits in terms of references.
Content Notes: Walliams is always making references to characters weight, and rarely in a positive way. I just find it ironic, in a book accept accepting peoples' differences. Yes, he discussed the fact that his dad was overweight due to his grief and subsequent comfort eating, which was somewhat refreshing. There is also a reference to the magazines his dad keeps under his bed, and how it may or may not make Dennis and his brother feel. Now I know that the range of things kids have access to on the internet these days, whether we like it or not, is so much more than any magazine, it may lead to some interesting questions!
Of course you can't discuss this book without addressing the 'cross-dressing'. I've read some reviews that criticised the book for 'grooming' and encouraging children to become cross-dressers. I disagree. I've also seen reviewers that criticise Walliams for continually emphasising Dennis' heterosexuality in his attraction to Lisa. I'm only one person, and of course there are a thousand ways to interpret a book (isn't that why we all love them?), but here's my two cents. Dennis is different than what his friends and family expect him to be, and he's terrified of everyone finding out. Lisa encourages him to be himself, and of course, inevitably his worst fears are realised. But that ending with the soccer match? Enough to bring a tear to anyone's eye. Most kids' prejudices come from other people and tend to be incredibly understanding of differences. And I think this is a book that can help them with that understanding.