"The little boy practices reading the magazine."
Translation:Cậu bé tập đọc tạp chí.
It's really saying that he's practising to read magazines in general, not any particular magazine. When you talk about a noun in general you don't need to insert the classifier. For example: "tôi thích mèo" (I like cats) or "tôi thường xuyên ăn gián" (I usually eat cockroaches).
my very own perception: "tập" is the general practice, involving training and repetition to acquire one skill; "luyện tập" requires on the other hand more effort, energy, work, sweat in order to sharpen a skill. a baby would "tập" walking, but an Olympian would "luyện tập" for his competitions.