If kids are not doing well and need extra credit especially, getting them interested in science in the first place may be the best bet. I always think if you can show the fun side of things, it will make you want to know the details (take Linear Algebra, if you only care about matrices on paper it's boring, but if you're talking about video games and rotating aliens it's much more fun). If they are interested in Asimov (Foundation and Robot series are always great starters), they may look to him later for his non-fiction - which he truly breaks down science topics better than anyone I've ever met (an extremely hard feat to accomplish). That being said, if there's room left, it may not hurt to have them read even a single chapter in one of his science non-fiction books, see all they learn in a single chapter to get them into it (and maybe buy the book for later). It's pain free reading and written so children can comprehend easily. He's the type of writer who doesn't need to show his intelligence by using every piece of tech jargon in his topics of study, he's the kind of writer who takes it a step further by knowing the topics in and out, then dispensing in a way only an expert writer and teacher could (he was a prof. before a writer.)
As an aside:
The whole reason I pursued an engineering/software career in the first place was a physics teacher in h.s. who the whole first year we just played with things and watched movies. I barely remember studying any text at all - but somehow retained so much I got college credit - without really trying. (I wasn't the only one by far.). I liken this to Asimov books. Thumbs up to teachers, you guys really do inspire us for the rest of our lives.