There are two different things that we call reading. The first is decoding; that is, the actual sounding out and pronouncing the words. The second is constructing meaning out of text. Many kids struggle so much with the decoding piece that they literally don't have enough energy and attention to get at the meaning. The girl I worked with today falls into this category. In the book we started reading today, Cam Jansen looked at her watch and thought, "I have to keep my parents at the park a little longer." The title of the book was The Birthday Mystery. I did a little probing to see if she could predict a surprise party coming up, but it took a few leading questions for her to get there. Students who are working hard at decoding can't make inferences or predictions about what will happen. They can't empathize with the characters. They can't engage in any kind of mental conversation with the author. They are just working too hard on decoding. Anything we can do to make reading more automatic frees up the brain to make meaning. That, "aha" moment that my student experienced this morning is the reason she should read at least a few more in the series. With every one that she reads she will have the experience of meeting old friends and familiar vocabulary. The more fluently she reads, the less of her brain she will have to devote to the hard work of decoding the words and the more of her brain she will be able to use on higher order skills like inference and prediction.
Most libraries now have a whole section devoted to series books and this is a great thing. Fifteen or so years ago, there was a real gap between Frog and Toad and books and real chapter books, but now, starting with the success of the Magic Tree House books there are many series written at a 2nd or 3rd grade reading level. (Arthur Adventures, Bailey School Kids,The Cobble Street Cousins, The Babysitters' Club and many, many others.) The sheer number of them shows how popular they are with emerging readers. They are uneven in quality and frankly as an adult reader, many of them are unspeakably boring. Don't feel guilty if you don't enjoy reading them aloud; that isn't what they are good for. Whether or not you think The Boxcar Children is a great read has nothing to do with whether it is a good book for your child to read. The great thing about picking up a new one of these books is that the child has the powerful experience of activating background knowledge to make reading easier and more pleasurable.
Think about it this way...would you rather get together with old friends over a casual meal or get all dressed up in uncomfortable clothes and high heels and meet a dozen new people you know nothing about? For most of us, the first is pleasure and the second is work. There are lots of good reasons to get dressed up and meet new people, but nobody wants to do it all the time. Our reading life is like that, too. I read many different kinds of books, but there are plenty of times when I don't feel like working at it. For a lighter read, I like mysteries by Donna Leon. These mysteries are set in Venice, a city I have visited. Commisario Guido Brunetti doesn't let any case get in the way of anticipating and enjoying a beautiful meal. . He and his wife are raising teenagers and dealing with problems I recognize For all these reasons it is easy and pleasurable to slip into one of these books. I know the characters, I can visualize the setting. It's like slipping into a pair of sweatpants.
So, if your child has found a book he or she loves and can't put down, the first thing to find out about it is whether it is part of a series. I love the idea that readers have books "on deck." If you can have the next 2 or 3 in the series at your fingertips, that is a great thing. I would argue for spending the money on some of these books just to have them accessible. When a certain book is hot at the library, but also the very next thing your child must read, it is worth it to keep the magic going. When my kids were in love with the Series of Unfortunate Events books there was a wait of months at the library. All four of my kids read the series and now most of them have been passed on to my nieces; so they have been well loved. After all, being able to share a great read is another readerly pleasure we want our kids to experience.