The Nate the Great series are perfect books for 1st grade boys (and girls...) They are not too long but they also do not have too many pictures. It would be good for girls, too. It's somewhat gender-neutral. It can be read in one sitting (about 15 - 30 minutes depending on how well your 1st grader is reading.) It does not have chapters, however. Because if this, it's tough to find a good place to "stop."