Is tomato a fruit or a vegetable? This debate has been going on for quite some time now, and it's an interesting one.
On one hand, everyone knows that you'd eat tomatoes with other vegetables like peppers or onions, maybe mushrooms. Also, tomatoes can be cooked in a variety of ways, but fruits are rarely cooked except in desserts. (Tomato pie, anyone?) People often eat a fruit raw and by itself, but who does that with a tomato? By such reasoning, tomatoes are vegetables.
On the other hand, fruits are defined as the parts of plants that contain seeds, whether small ones as on strawberries or large cores as in peaches. Tomatoes have seeds, therefore they are fruit. The same can be said with other pseudo-vegetables like cucumbers, squash, and green beans, by the way.
So which is correct? The answer: it depends. What's interesting about this debate is that the two sides are talking about two separate things; the context is different. I'd say they're comparing apples to oranges, but we don't need to add more fruit to this situation.
You'll notice the argument that tomatoes are vegetables is all about cooking and eating. Within the context of food, tomatoes are vegetables. But the context of the opposing argument has nothing to do with food; within the context of plants, tomatoes are fruit. So the answer to this timeless question depends on whether you're asking a chef or a botanist. In other words, this debate is pointless, but it exists because sometimes we don't pay attention to context.
In the classroom, identifying and clearly expressing context is crucial. Sometimes it's up to you as the teacher to clarify the context when confusion arises over the meaning of a word, phrase, or sentence. And when teaching something new, it's typically best to establish the context (hopefully, something your students are already familiar with) before introducing the new element. If they already know the context, it'll be much easier for them to grasp the meaning or significance of whatever you're teaching.
The students themselves also need to establish context. The biggest problem I've seen regarding this is in writing assignments - essays, for example. When given an essay prompt in an exam, students typically start writing without restating the prompt, assuming that whoever reads it already knows what to expect. This isn't always the case, and even though readers do sometimes know the exact prompt, leaving out the context isn't a habit students should get into. It doesn't take much; just a brief line is usually all it takes. Communicating in the real world relies a lot upon establishing context, so students need to learn how to do this well in the classroom.
When you're facing some confusion in the classroom, consider whether the context was properly made known. Better yet, make sure everyone is in the habit of expressing the context at the beginning to avoid any confusion in the first place. Context matters.