Crossword books show most clearly how the completion rule at 3.4 really works. A crossword book is almost entirely blank squares waiting to be filled in, so a literal reading of the quarter rule would standard-rate it. It does not, for the same reason school workbooks do not: the spaces are incidental to the essential character of the book, and the book is what you bought. Activity books that combine colouring with puzzles and quizzes are zero-rated under 3.8 as well. The limit is the same one that applies to children's books generally: where the pages are boards for games, it is a game, and games are standard-rated.
What decides it?
Whether the blanks are part of a book, or the thing is really a game.
Is the design and artwork for crossword and puzzle books zero-rated too?
If your printer does the design, typesetting or finishing as part of the same zero-rated print job, that work can be zero-rated too. Design bought separately from a studio is a standard-rated service.
Where does this come from?
HMRC VAT Notice 701/10, section 8, HMRC's guidance on zero rating books and printed matter. See the notices we work from.
Some real jobs
A book of 100 crosswords0%
Crossword books are listed as zero-rated despite being mostly space for completion.
A children's activity book of puzzles and colouring0%
3.8 names activity books combining colouring with puzzles and the like.
A book whose pages are game boards20%
3.7 standard-rates items where the pages are boards for games.
